TCS NQT 2027 Recently Asked Questions – 5th & 9th June Assessment | Coding Solutions

import java.util.HashMap;

public class Solution {
    public static int[] coinPairIndices(int[] coins, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < coins.length; i++) {
            int complement = target - coins[i];
            if (map.containsKey(complement)) {
                return new int[] { map.get(complement), i };
            }
            map.put(coins[i], i);
        }
        return new int[] { -1, -1 }; // no pair found
    }

    public static void main(String[] args) {
        int[] coins = {2, 7, 11, 15};
        int[] result = coinPairIndices(coins, 9);
        System.out.println("[" + result[0] + ", " + result[1] + "]"); // [0, 1]
    }
}

#include <iostream>
#include <vector>
#include <unordered_map>
using namespace std;

vector<int> coinPairIndices(vector<int>& coins, int target) {
    unordered_map<int, int> mp;
    for (int i = 0; i < coins.size(); i++) {
        int complement = target - coins[i];
        if (mp.count(complement))
            return { mp[complement], i };
        mp[coins[i]] = i;
    }
    return { -1, -1 };
}

int main() {
    vector<int> coins = {2, 7, 11, 15};
    auto res = coinPairIndices(coins, 9);
    cout << "[" << res[0] << ", " << res[1] << "]" << endl; // [0, 1]
}

def coin_pair_indices(coins, target):
    seen = {}
    for i, val in enumerate(coins):
        complement = target - val
        if complement in seen:
            return [seen[complement], i]
        seen[val] = i
    return [-1, -1]

# Test
coins = [2, 7, 11, 15]
print(coin_pair_indices(coins, 9))  # [0, 1]

import java.util.Arrays;

public class MergeArrays {
    public static int[] mergeSorted(int[] A, int[] B) {
        // Reverse B to make it ascending
        int left = 0, right = B.length - 1;
        while (left < right) {
            int tmp = B[left]; B[left] = B[right]; B[right] = tmp;
            left++; right--;
        }
        // Two-pointer merge
        int[] result = new int[A.length + B.length];
        int i = 0, j = 0, k = 0;
        while (i < A.length && j < B.length)
            result[k++] = A[i] <= B[j] ? A[i++] : B[j++];
        while (i < A.length) result[k++] = A[i++];
        while (j < B.length) result[k++] = B[j++];
        return result;
    }

    public static void main(String[] args) {
        int[] A = {1,3,5,7}, B = {10,8,6,4};
        System.out.println(Arrays.toString(mergeSorted(A, B)));
        // [1, 3, 4, 5, 6, 7, 8, 10]
    }
}

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

vector<int> mergeSorted(vector<int> A, vector<int> B) {
    reverse(B.begin(), B.end());
    vector<int> result;
    int i = 0, j = 0;
    while (i < A.size() && j < B.size())
        result.push_back(A[i] <= B[j] ? A[i++] : B[j++]);
    while (i < A.size()) result.push_back(A[i++]);
    while (j < B.size()) result.push_back(B[j++]);
    return result;
}

int main() {
    vector<int> A = {1,3,5,7}, B = {10,8,6,4};
    for (auto v : mergeSorted(A, B)) cout << v << " ";
    // 1 3 4 5 6 7 8 10
}

def merge_sorted(A, B):
    B_asc = B[::-1]   # reverse B to ascending
    result = []
    i = j = 0
    while i < len(A) and j < len(B_asc):
        if A[i] <= B_asc[j]:
            result.append(A[i]); i += 1
        else:
            result.append(B_asc[j]); j += 1
    result.extend(A[i:])
    result.extend(B_asc[j:])
    return result

print(merge_sorted([1,3,5,7], [10,8,6,4]))
# [1, 3, 4, 5, 6, 7, 8, 10]

public class FirstOccurrence {
    public static int firstOccurrence(int[] arr, int target) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == target) return i;
        }
        return -1;
    }

    public static void main(String[] args) {
        int[] arr = {4, 2, 7, 2, 9, 2};
        System.out.println(firstOccurrence(arr, 2)); // 1
        System.out.println(firstOccurrence(arr, 3)); // -1
    }
}

#include <iostream>
#include <vector>
using namespace std;

int firstOccurrence(vector<int>& arr, int target) {
    for (int i = 0; i < arr.size(); i++)
        if (arr[i] == target) return i;
    return -1;
}

int main() {
    vector<int> arr = {4,2,7,2,9,2};
    cout << firstOccurrence(arr, 2) << endl; // 1
    cout << firstOccurrence(arr, 3) << endl; // -1
}

def first_occurrence(arr, target):
    for i, val in enumerate(arr):
        if val == target:
            return i
    return -1

print(first_occurrence([4,2,7,2,9,2], 2))  # 1
print(first_occurrence([5,8,1,6], 3))          # -1

import java.util.LinkedList;
import java.util.Queue;

public class MinDepth {
    static class TreeNode {
        int val;
        TreeNode left, right;
        TreeNode(int v) { val = v; }
    }

    public static int minDepth(TreeNode root) {
        if (root == null) return 0;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        int depth = 1;
        while (!q.isEmpty()) {
            int size = q.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = q.poll();
                if (node.left == null && node.right == null)
                    return depth; // leaf reached!
                if (node.left  != null) q.offer(node.left);
                if (node.right != null) q.offer(node.right);
            }
            depth++;
        }
        return depth;
    }

    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(4);
        System.out.println(minDepth(root)); // 2
    }
}

#include <iostream>
#include <queue>
using namespace std;

struct TreeNode {
    int val;
    TreeNode *left, *right;
    TreeNode(int v) : val(v), left(nullptr), right(nullptr) {}
};

int minDepth(TreeNode* root) {
    if (!root) return 0;
    queue<TreeNode*> q;
    q.push(root);
    int depth = 1;
    while (!q.empty()) {
        int sz = q.size();
        for (int i = 0; i < sz; i++) {
            auto node = q.front(); q.pop();
            if (!node->left && !node->right) return depth;
            if (node->left)  q.push(node->left);
            if (node->right) q.push(node->right);
        }
        depth++;
    }
    return depth;
}

int main() {
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    cout << minDepth(root) << endl; // 2
}

from collections import deque

class TreeNode:
    def __init__(self, val=0):
        self.val = val
        self.left = self.right = None

def min_depth(root):
    if not root: return 0
    q = deque([(root, 1)])
    while q:
        node, depth = q.popleft()
        if not node.left and not node.right:
            return depth   # leaf!
        if node.left:  q.append((node.left,  depth + 1))
        if node.right: q.append((node.right, depth + 1))

# Build: 1 → (2→4, 3)
root = TreeNode(1)
root.left, root.right = TreeNode(2), TreeNode(3)
root.left.left = TreeNode(4)
print(min_depth(root))  # 2

TCS NQT Python Coding Questions 2026

n = int(input())
arr = [int(input()) for _ in range(n)]
pos = 0
for x in arr:
    if x != 0:
        arr[pos] = x
        pos += 1
while pos < n:
    arr[pos] = 0
    pos += 1
print(*arr)

day = input().strip().lower()
n = int(input())
days = {"mon":0,"tue":1,"wed":2,"thu":3,"fri":4,"sat":5,"sun":6}
d = days[day]
to_sun = (6 - d) % 7
if to_sun >= n:
    print(0)
else:
    print(1 + (n - to_sun - 1) // 7)

n = int(input())
prices = [int(input()) for _ in range(n)]
min_price = float('inf')
max_profit = 0
for p in prices:
    min_price = min(min_price, p)
    max_profit = max(max_profit, p - min_price)
print(max_profit)

t = int(input())
for _ in range(t):
    n = int(input())
    print(n * (n - 1) // 2)

s = input().strip()
L = int(input())
best = 0
for i in range(0, len(s), L):
    best = max(best, s[i:i+L].count('a'))
print(best)

n = int(input())
r = int(input())
if r == 0:
    print(0)
else:
    for _ in range(r):
        n = sum(int(d) for d in str(n))
        if n < 10:
            break
    print(n)

n = int(input())
arr = [int(input()) for _ in range(n)]
result = 0
for x in arr:
    result ^= x
print(result)

n = int(input())
arr = [int(input()) for _ in range(n)]
low = mid = 0
high = n - 1
while mid <= high:
    if arr[mid] == 0:
        arr[low], arr[mid] = arr[mid], arr[low]
        low += 1; mid += 1
    elif arr[mid] == 2:
        arr[mid], arr[high] = arr[high], arr[mid]
        high -= 1
    else:
        mid += 1
print(*arr)

import math
n = int(input())
print(2 * math.factorial(n - 2))

n = int(input())
mask = (1 << n.bit_length()) - 1
print(n ^ mask)

n = int(input())
sets = [set(input().strip()) for _ in range(n)]
common = sets[0]
for s in sets[1:]:
    common &= s
print(len(common))

n = int(input())
arr = [int(input()) for _ in range(n)]
count = 1
mx = arr[0]
for x in arr[1:]:
    if x > mx:
        count += 1
        mx = x
print(count)

fname = input().strip()
valid_ext = {"exe","pdf","txt","py","java"}
if " " in fname or fname.count(".") != 1:
    print("Invalid")
else:
    name, ext = fname.split(".")
    if name and name[0].isalnum() and ext in valid_ext:
        print("Valid")
    else:
        print("Invalid")

import math
n = int(input())
print(math.factorial(n))

n = int(input())
days_list = list(map(int, input().split()))
total = 0
for d in days_list:
    if d <= 0:
        continue
    elif d <= 5:
        total += 5 * d
    elif d <= 10:
        total += 25 + 10 * (d - 5)
    else:
        total += 25 + 50 + 20 * (d - 10)
print(total)

n = int(input())
arr = [int(input()) for _ in range(n)]
unique = sorted(set(arr), reverse=True)
print(unique[1] if len(unique) >= 2 else -1)

n = int(input())
arr = [int(input()) for _ in range(n)]
print(*arr[::-1])

n = int(input())
arr = [int(input()) for _ in range(n)]
seen = set()
result = []
for x in arr:
    if x not in seen:
        seen.add(x)
        result.append(x)
print(*result)

n = int(input())
arr = [int(input()) for _ in range(n)]
k = int(input())
seen = set()
pairs = set()
for x in arr:
    comp = k - x
    if comp in seen:
        pair = (min(x,comp), max(x,comp))
        if pair not in pairs:
            print(pair)
            pairs.add(pair)
    seen.add(x)

from collections import OrderedDict
n = int(input())
arr = [int(input()) for _ in range(n)]
freq = OrderedDict()
for x in arr:
    freq[x] = freq.get(x, 0) + 1
for k, v in freq.items():
    print(f"{k}:{v}")

n = int(input())
arr = [int(input()) for _ in range(n)]
cur = max_s = arr[0]
for x in arr[1:]:
    cur = max(x, cur + x)
    max_s = max(max_s, cur)
print(max_s)

n = int(input())
arr = [int(input()) for _ in range(n)]
k = int(input()) % n
if k:
    arr = arr[-k:] + arr[:-k]
print(*arr)

n = int(input())
arr = [int(input()) for _ in range(n-1)]
print(n*(n+1)//2 - sum(arr))

n = int(input())
nums = [int(input()) for _ in range(n)]
slow = fast = nums[0]
while True:
    slow = nums[slow]
    fast = nums[nums[fast]]
    if slow == fast:
        break
slow = nums[0]
while slow != fast:
    slow = nums[slow]
    fast = nums[fast]
print(slow)

n = int(input())
arr = [int(input()) for _ in range(n)]
num_set = set(arr)
best = 0
for x in num_set:
    if x - 1 not in num_set:
        cur, streak = x, 1
        while cur + 1 in num_set:
            cur += 1
            streak += 1
        best = max(best, streak)
print(best)

s = input().strip().lower()
print("Yes" if s == s[::-1] else "No")

from collections import Counter
s1 = input().strip().lower()
s2 = input().strip().lower()
print("Yes" if Counter(s1) == Counter(s2) else "No")

s = input().strip().lower()
v = sum(1 for c in s if c in 'aeiou')
con = sum(1 for c in s if c.isalpha() and c not in 'aeiou')
print(f"V:{v} C:{con}")

from collections import Counter
s = input().strip()
freq = Counter(s)
for c in s:
    if freq[c] == 1:
        print(c)
        break
else:
    print(-1)

s = input()
print(' '.join(s.split()[::-1]))

s = input().strip()
seen = set()
left = max_len = 0
for right, c in enumerate(s):
    while c in seen:
        seen.remove(s[left])
        left += 1
    seen.add(c)
    max_len = max(max_len, right - left + 1)
print(max_len)

text = input().strip()
pat = input().strip()
count = sum(1 for i in range(len(text)-len(pat)+1)
            if text[i:i+len(pat)] == pat)
print(count)

s = input().strip()
if not s:
    print(s)
else:
    res = []
    count = 1
    for i in range(1, len(s)):
        if s[i] == s[i-1]:
            count += 1
        else:
            res.append(s[i-1] + (str(count) if count > 1 else ""))
            count = 1
    res.append(s[-1] + (str(count) if count > 1 else ""))
    compressed = "".join(res)
    print(compressed if len(compressed) < len(s) else s)

s1 = input().strip()
s2 = input().strip()
print("Yes" if len(s1)==len(s2) and s2 in s1+s1 else "No")

n = int(input())
strs = [input().strip() for _ in range(n)]
strs.sort()
prefix = []
for a, b in zip(strs[0], strs[-1]):
    if a == b:
        prefix.append(a)
    else:
        break
print(''.join(prefix) if prefix else "")

n = int(input())
def is_prime(n):
    if n < 2: return False
    for i in range(2, int(n**0.5)+1):
        if n % i == 0: return False
    return True
print("Prime" if is_prime(n) else "Not Prime")

from math import gcd
a, b = int(input()), int(input())
g = gcd(a, b)
print(f"GCD:{g} LCM:{(a*b)//g}")

n = int(input())
digits = str(n)
k = len(digits)
print("Yes" if n == sum(int(d)**k for d in digits) else "No")

n = int(input())
a, b = 0, 1
fib = []
for _ in range(n):
    fib.append(a)
    a, b = b, a + b
print(*fib)

n = int(input())
result = 1
for i in range(2, n+1):
    result *= i
print(result)

n = int(input())
total = sum(i for i in range(1, n) if n % i == 0)
print("Yes" if total == n else "No")

n = int(input())
print(bin(n)[2:], oct(n)[2:], hex(n)[2:])

n = int(input())
factors = []
d = 2
while d * d <= n:
    while n % d == 0:
        factors.append(d)
        n //= d
    d += 1
if n > 1:
    factors.append(n)
print(*factors)

b, e = int(input()), int(input())
result = 1
base = b
while e > 0:
    if e % 2 == 1:
        result *= base
    base *= base
    e //= 2
print(result)

n = int(input())
print(0 if n == 0 else 1 + (n - 1) % 9)

n = int(input())
arr = [int(input()) for _ in range(n)]
for i in range(n):
    for j in range(0, n-i-1):
        if arr[j] > arr[j+1]:
            arr[j], arr[j+1] = arr[j+1], arr[j]
print(*arr)

n = int(input())
arr = [int(input()) for _ in range(n)]
t = int(input())
low, high, result = 0, n-1, -1
while low <= high:
    mid = (low + high) // 2
    if arr[mid] == t:
        result = mid; break
    elif arr[mid] < t:
        low = mid + 1
    else:
        high = mid - 1
print(result)

n = int(input())
arr = [int(input()) for _ in range(n)]
k = int(input())
arr.sort(reverse=True)
print(arr[k-1])

m = int(input())
a = [int(input()) for _ in range(m)]
n = int(input())
b = [int(input()) for _ in range(n)]
i = j = 0
res = []
while i < m and j < n:
    if a[i] <= b[j]:
        res.append(a[i]); i += 1
    else:
        res.append(b[j]); j += 1
res.extend(a[i:])
res.extend(b[j:])
print(*res)

n = int(input())
arr = [int(input()) for _ in range(n)]
passes = 0
for i in range(n):
    swapped = False
    for j in range(0, n-i-1):
        if arr[j] > arr[j+1]:
            arr[j], arr[j+1] = arr[j+1], arr[j]
            swapped = True
    if swapped:
        passes += 1
    else:
        break
print(passes)

n = int(input())
for i in range(1, n+1):
    print("*" * i)

n = int(input())
for i in range(1, n+1):
    print(*range(1, i+1))

n = int(input())
for i in range(n, 0, -1):
    print("*" * i)

n = int(input())
for i in range(1, n+1, 2):
    print(" " * ((n-i)//2) + "*" * i)
for i in range(n-2, 0, -2):
    print(" " * ((n-i)//2) + "*" * i)

def hanoi(n, src, dest, aux):
    if n == 1:
        print(f"{src}->{dest}")
        return
    hanoi(n-1, src, aux, dest)
    print(f"{src}->{dest}")
    hanoi(n-1, aux, dest, src)

n = int(input())
hanoi(n, "A", "C", "B")

s1 = input().strip()
s2 = input().strip()
m, n = len(s1), len(s2)
dp = [[0]*(n+1) for _ in range(m+1)]
for i in range(1, m+1):
    for j in range(1, n+1):
        if s1[i-1] == s2[j-1]:
            dp[i][j] = dp[i-1][j-1] + 1
        else:
            dp[i][j] = max(dp[i-1][j], dp[i][j-1])
print(dp[m][n])

n, c = int(input()), int(input())
w = list(map(int, input().split()))
v = list(map(int, input().split()))
dp = [[0]*(c+1) for _ in range(n+1)]
for i in range(1, n+1):
    for cap in range(c+1):
        dp[i][cap] = dp[i-1][cap]
        if w[i-1] <= cap:
            dp[i][cap] = max(dp[i][cap],
                             dp[i-1][cap-w[i-1]] + v[i-1])
print(dp[n][c])

def count_subsets(arr, n, s):
    if s == 0: return 1
    if n == 0: return 0
    if arr[n-1] > s:
        return count_subsets(arr, n-1, s)
    return (count_subsets(arr, n-1, s) +
            count_subsets(arr, n-1, s - arr[n-1]))

n = int(input())
arr = list(map(int, input().split()))
s = int(input())
print(count_subsets(arr, n, s))

text = input()
k = int(input()) % 26
result = []
for c in text:
    if c.isalpha():
        base = ord('A') if c.isupper() else ord('a')
        result.append(chr((ord(c) - base + k) % 26 + base))
    else:
        result.append(c)
print(''.join(result))

y = int(input())
if (y % 4 == 0 and y % 100 != 0) or (y % 400 == 0):
    print("Leap Year")
else:
    print("Not Leap Year")

Top 200 Infosys Verbal Ability Questions SE, DSE & SP Roles — With Answers

Top 100 Questions Asked in Cognizant Online Assessment

TCS Interview Questions 2026 – Real HR, Technical & Managerial Round Questions

TCS Interview Questions 2026: Real HR, Technical and Managerial Round Questions

TCS NQT — 100 ACTUAL INTERVIEW QUESTIONS WITH ANSWERS

SQL | OOPs | DBMS | OS | Networks | Coding | Behavioural | Managerial | HR

Digital & Prime Level | All Actually Asked

📋 CATEGORY MAP

🔷 SQL — Q1 to Q12

Q1. ⭐ Write a SQL query to find the second highest salary from the Employee table.

Answer:

-- Method 1: Subquery
SELECT MAX(salary) AS SecondHighest
FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);

-- Method 2: DENSE_RANK (handles duplicates correctly)
SELECT salary FROM (
  SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) AS rnk
  FROM employees
) t WHERE rnk = 2;

-- Method 3: LIMIT OFFSET (MySQL)
SELECT DISTINCT salary FROM employees
ORDER BY salary DESC
LIMIT 1 OFFSET 1;

Q2. ⭐ What is the difference between WHERE and HAVING clause?

Answer:

-- WHERE filters rows before grouping
SELECT dept, AVG(salary) FROM employees
WHERE salary > 20000
GROUP BY dept
HAVING AVG(salary) > 50000;
-- HAVING filters after grouping

Q3. ⭐ What are the different types of JOINs? Explain with example.

Answer:

INNER JOIN — Only matching rows from both tables.

SELECT e.name, d.dept_name
FROM employees e INNER JOIN departments d ON e.dept_id = d.id;

LEFT JOIN — All rows from left table + matching from right (NULL if no match).

SELECT e.name, d.dept_name
FROM employees e LEFT JOIN departments d ON e.dept_id = d.id;

RIGHT JOIN — All rows from right table + matching from left.

FULL OUTER JOIN — All rows from both tables (NULL where no match).

SELF JOIN — Table joined with itself.

SELECT a.name AS employee, b.name AS manager
FROM employees a JOIN employees b ON a.manager_id = b.id;

CROSS JOIN — Cartesian product of both tables.

Q4. ⭐ What is the difference between DELETE, TRUNCATE, and DROP?

Answer:

DELETE FROM employees WHERE id = 5;   -- removes specific row
TRUNCATE TABLE employees;              -- removes all rows, keeps structure
DROP TABLE employees;                  -- removes table completely

Q5. ⭐ What is the difference between DDL, DML, DCL, and TCL?

Answer:

DDL (Data Definition Language) — Defines structure. Commands: CREATE, ALTER, DROP, TRUNCATE, RENAME

DML (Data Manipulation Language) — Manipulates data. Commands: INSERT, UPDATE, DELETE, SELECT

DCL (Data Control Language) — Controls access. Commands: GRANT, REVOKE

TCL (Transaction Control Language) — Manages transactions. Commands: COMMIT, ROLLBACK, SAVEPOINT

Q6. ⭐ Write a query to find all employees whose name starts with ‘A’.

Answer:

SELECT * FROM employees
WHERE name LIKE 'A%';

-- Other LIKE patterns:
-- LIKE '%A'   → ends with A
-- LIKE '%A%'  → contains A anywhere
-- LIKE '_A%'  → second character is A

Q7. ⭐ What is a GROUP BY clause? Write a query to find department-wise employee count.

Answer: GROUP BY groups rows with the same values into summary rows.

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department
ORDER BY employee_count DESC;

-- With HAVING to filter groups:
SELECT department, COUNT(*) AS cnt
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

Q8. ⭐ What is a subquery? What are its types?

Answer: A subquery is a query nested inside another query.

Types:

• Single-row subquery — returns one row: WHERE salary = (SELECT MAX(salary) FROM employees)
• Multi-row subquery — returns multiple rows: WHERE dept_id IN (SELECT id FROM departments WHERE location = 'Mumbai')
• Correlated subquery — references outer query: executes once per outer row
• Scalar subquery — returns single value, used in SELECT list

-- Correlated subquery example:
SELECT name FROM employees e
WHERE salary > (SELECT AVG(salary) FROM employees WHERE dept_id = e.dept_id);

Q9. ⭐ What is an INDEX in SQL? What are its advantages and disadvantages?

Answer: An index is a data structure (usually B-Tree) that speeds up data retrieval from a table.

CREATE INDEX idx_salary ON employees(salary);
CREATE UNIQUE INDEX idx_email ON employees(email);

Advantages:

• Faster SELECT and WHERE query performance
• Faster sorting and ordering

Disadvantages:

• Slows down INSERT, UPDATE, DELETE (index must be updated)
• Consumes additional disk space

When NOT to use: Small tables, columns with many NULL values, columns rarely used in WHERE clauses.

Q10. ⭐ What are aggregate functions in SQL? Give examples.

Answer: Aggregate functions perform calculations on a set of values and return a single value.

SELECT dept, COUNT(*) AS headcount, AVG(salary) AS avg_sal,
       MAX(salary) AS max_sal, MIN(salary) AS min_sal
FROM employees
GROUP BY dept;

Q11. ⭐ What is the difference between UNION and UNION ALL?

Answer:

SELECT name FROM employees_india
UNION
SELECT name FROM employees_usa;  -- unique names only

SELECT name FROM employees_india
UNION ALL
SELECT name FROM employees_usa;  -- all names including duplicates

Q12. ⭐ Write a SQL query to find employees who earn more than the average salary.

Answer:

SELECT name, salary
FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees)
ORDER BY salary DESC;

-- With department-wise average:
SELECT e.name, e.salary, e.department
FROM employees e
WHERE e.salary > (
    SELECT AVG(salary) FROM employees
    WHERE department = e.department
)
ORDER BY e.department, e.salary DESC;

🟠 OOPs — Q13 to Q24

Q13. ⭐ What are the four pillars of OOPs? Explain each with a real-life example.

Answer:

Encapsulation — Wrapping data and methods into a single unit (class) and restricting direct access to data. Real-life: A medicine capsule hides its contents. You take it without knowing what’s inside.

class BankAccount {
    private double balance;          // hidden data
    public double getBalance() { return balance; }  // controlled access
    public void deposit(double amt) { if(amt > 0) balance += amt; }
}

Abstraction — Hiding implementation details, showing only what is necessary. Real-life: You drive a car without knowing how the engine works internally.

abstract class Shape {
    abstract double area();  // what — not how
}
class Circle extends Shape {
    double r;
    double area() { return 3.14 * r * r; }
}

Inheritance — A child class acquires properties and behaviours of a parent class. Real-life: A child inherits traits (eye colour, height) from parents.

class Animal { void eat() { System.out.println("eating"); } }
class Dog extends Animal { void bark() { System.out.println("Woof"); } }

Polymorphism — Same method name behaves differently based on context. Real-life: A person acts differently as a parent, employee, and friend.

• Compile-time (Overloading): same method name, different parameters
• Run-time (Overriding): child class redefines parent method

Q14. ⭐ What is the difference between an abstract class and an interface?

Answer:

abstract class Vehicle {
    String brand;                   // instance variable
    abstract void start();          // must override
    void fuel() { System.out.println("needs fuel"); }  // concrete
}
interface Electric { void charge(); }
class Tesla extends Vehicle implements Electric {
    void start() { System.out.println("silent start"); }
    public void charge() { System.out.println("charging"); }
}

Q15. ⭐ What is the difference between method overloading and method overriding?

Answer:

// Overloading — same class
class Calculator {
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }  // different params
}

// Overriding — child class
class Animal { void sound() { System.out.println("..."); } }
class Cat extends Animal {
    @Override
    void sound() { System.out.println("Meow"); }  // same signature
}

Q16. ⭐ What is a constructor? What are its types? Can a constructor be private?

Answer: A constructor is a special method called when an object is created. It has the same name as the class and no return type.

Types:

• Default constructor — No parameters; provided by Java if no constructor defined
• Parameterised constructor — Takes arguments to initialise fields
• Copy constructor — Creates object by copying another object (C++ has it natively)

Can a constructor be private? Yes — used in Singleton Pattern to prevent external instantiation.

class Singleton {
    private static Singleton instance;
    private Singleton() { }               // private constructor
    public static Singleton getInstance() {
        if (instance == null)
            instance = new Singleton();
        return instance;
    }
}

Q17. ⭐ What is the difference between this and super keyword?

Answer:

class Animal {
    String name;
    Animal(String name) { this.name = name; }
    void display() { System.out.println("Animal: " + name); }
}
class Dog extends Animal {
    String breed;
    Dog(String name, String breed) {
        super(name);           // calls Animal constructor
        this.breed = breed;    // refers to Dog's own field
    }
    void display() {
        super.display();       // calls Animal's display()
        System.out.println("Breed: " + breed);
    }
}

Q18. ⭐ What is a virtual function? What is a pure virtual function?

Answer: Virtual function — A function in base class declared with virtual keyword. Enables run-time polymorphism — the correct overridden version is called through a base class pointer/reference.

Pure virtual function — A virtual function with no body (= 0). Makes the class abstract — cannot be instantiated. Any derived class MUST override it.

class Shape {
public:
    virtual void draw() { cout << "drawing shape"; }    // virtual
    virtual double area() = 0;                           // pure virtual
};
class Circle : public Shape {
public:
    void draw() override { cout << "drawing circle"; }
    double area() override { return 3.14 * r * r; }
private:
    double r = 5;
};
// Shape s;    // ERROR — cannot instantiate abstract class
Circle c;      // OK — all pure virtual functions overridden

Q19. ⭐ What is a destructor? When is it called?

Answer: A destructor is a special method that is automatically called when an object goes out of scope or is explicitly deleted. It cleans up resources (memory, file handles, connections) allocated by the object.

class FileHandler {
    FILE* fp;
public:
    FileHandler(const char* name) { fp = fopen(name, "r"); }
    ~FileHandler() {                  // destructor
        if (fp) fclose(fp);           // auto cleanup
        cout << "File closed";
    }
};
// Destructor called automatically when object scope ends

Key points:

• Name = ~ClassName()
• No parameters, no return type
• Called in reverse order of construction
• In Java, finalize() plays a similar role (but garbage collector handles most cleanup)

Q20. ⭐ What is multiple inheritance? Why doesn’t Java support it?

Answer: Multiple inheritance — A class inheriting from more than one parent class.

Java doesn’t support multiple inheritance for classes because of the Diamond Problem:

    A
   / \
  B   C
   \ /
    D  ← Which version of A's method should D use?

If B and C both override a method from A, and D inherits from both B and C, it’s ambiguous which version D should call.

Java’s solution: Java allows multiple inheritance through interfaces (since interfaces had no implementation in Java 7; Java 8 default methods have explicit resolution rules).

interface B { default void show() { System.out.println("B"); } }
interface C { default void show() { System.out.println("C"); } }
class D implements B, C {
    public void show() { B.super.show(); }  // explicitly resolve conflict
}

Q21. ⭐ What is the difference between composition and inheritance? When to use which?

Answer:

// Inheritance (IS-A)
class Dog extends Animal { }

// Composition (HAS-A) — preferred over inheritance
class Car {
    private Engine engine;       // Car HAS-A Engine
    private Wheels wheels;
    Car() { engine = new Engine(); wheels = new Wheels(); }
}

Rule: Prefer composition over inheritance (GoF principle). Use inheritance only when there’s a genuine IS-A relationship that won’t change.

Q22. ⭐ What is the concept of encapsulation? How is it achieved in Java?

Answer: Encapsulation = bundling data (fields) and methods that operate on data into a single unit (class), and restricting direct access to the internal state.

Achieved through:

1. Making fields private
2. Providing public getter/setter methods with validation logic

class Employee {
    private String name;
    private double salary;

    public String getName() { return name; }
    public void setName(String name) {
        if (name != null && !name.isEmpty())
            this.name = name;
    }
    public double getSalary() { return salary; }
    public void setSalary(double salary) {
        if (salary > 0) this.salary = salary;    // validation
    }
}

Benefits: Data hiding, controlled access, easier maintenance, increased flexibility.

Q23. ⭐ Is C++ a purely object-oriented language? Is Java?

Answer: C++: NOT purely object-oriented. Reasons:

• You can write functions outside classes
• Has primitive data types (int, char, float) which are not objects
• main() exists outside any class
• Supports procedural programming

Java: NOT purely object-oriented either (despite common belief). Reasons:

• Has primitive data types (int, long, double, boolean) which are not objects
• Static methods can be called without creating objects
• However, Java is MORE object-oriented than C++

Purely OOP languages: Smalltalk, Ruby — where everything including numbers are objects.

Q24. ⭐ What is the difference between a class and an object?

Answer:

// Class — blueprint (defined once)
class Car {
    String brand;
    int speed;
    void drive() { System.out.println("driving " + brand); }
}

// Objects — instances (created many times)
Car c1 = new Car();  c1.brand = "Tesla";
Car c2 = new Car();  c2.brand = "BMW";
// c1 and c2 are separate objects of the same class

🟡 DBMS — Q25 to Q36

Q25. ⭐ What is normalization? Explain 1NF, 2NF, 3NF, and BCNF.

Answer: Normalization organises a database to reduce data redundancy and improve data integrity.

1NF (First Normal Form):

• Atomic values — no multi-valued or composite attributes
• Each column has a single value per row
• Violation: Phone: 9876543210, 9123456789 in one cell

2NF (Second Normal Form):

• Must be 1NF
• No partial dependency — every non-key attribute must depend on the FULL primary key
• Applies only to composite primary keys

3NF (Third Normal Form):

• Must be 2NF
• No transitive dependency — non-key column should NOT depend on another non-key column
• Example violation: EmpID → Dept → DeptLocation (DeptLocation depends on Dept, not EmpID)

BCNF (Boyce-Codd Normal Form):

• Stronger version of 3NF
• For every functional dependency X → Y, X must be a super key

Q26. ⭐ What is the difference between a primary key and a unique key?

Answer:

CREATE TABLE employees (
    emp_id INT PRIMARY KEY,       -- primary key
    email VARCHAR(100) UNIQUE,    -- unique key
    aadhar VARCHAR(12) UNIQUE     -- another unique key
);

Q27. ⭐ What is a foreign key? What is referential integrity?

Answer: A foreign key is a column in one table that references the primary key of another table. It creates a link between two tables.

Referential Integrity ensures that:

• You cannot insert a foreign key value that doesn’t exist in the referenced table
• You cannot delete a primary key row that is referenced by a foreign key (unless CASCADE is set)

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(id)
        ON DELETE CASCADE     -- delete orders when customer is deleted
        ON UPDATE CASCADE     -- update if customer id changes
);

Q28. ⭐ What are the two integrity rules in DBMS?

Answer: (Actual TCS Prime question — PrepInsta)

1. Entity Integrity Rule: Every table must have a primary key, and the primary key column cannot contain NULL values. Every row must be uniquely identifiable.

2. Referential Integrity Rule: Foreign key values must either:

• Match a primary key value in the referenced table, OR
• Be NULL

This prevents orphaned records — you cannot have an Order referencing a Customer that doesn’t exist.

Q29. ⭐ What is a transaction in DBMS? What are ACID properties?

Answer: A transaction is a sequence of database operations treated as a single logical unit.

A — Atomicity: All-or-nothing. If any step fails, the entire transaction rolls back. Example: Bank transfer — deduct from A AND credit to B must both succeed or both fail.

C — Consistency: Transaction takes DB from one valid state to another, maintaining all constraints.

I — Isolation: Concurrent transactions don’t interfere. Intermediate states are invisible to others.

D — Durability: Once committed, changes are permanent — survive system crashes (via write-ahead log).

Q30. ⭐ What is a view in SQL? What are its advantages?

Answer: A view is a virtual table based on a SELECT query. It doesn’t store data physically — it stores the query definition.

-- Create a view
CREATE VIEW high_earners AS
SELECT name, department, salary
FROM employees
WHERE salary > 80000;

-- Use it like a table
SELECT * FROM high_earners WHERE department = 'Engineering';

Advantages:

• Security — hide sensitive columns from users
• Simplification — complex queries stored once, reused as simple table
• Data abstraction — underlying table structure can change without affecting users
• Aggregation — precompute frequently needed aggregations

Q31. ⭐ What is the difference between clustered and non-clustered index?

Answer:

-- Clustered (primary key creates it automatically)
CREATE TABLE emp (id INT PRIMARY KEY, name VARCHAR(50));

-- Non-clustered
CREATE INDEX idx_name ON emp(name);
CREATE INDEX idx_dept_sal ON emp(department, salary);  -- composite

Q32. ⭐ What is a trigger in SQL? When is it used?

Answer: A trigger is a stored procedure that automatically executes in response to a DML event (INSERT, UPDATE, DELETE) on a table.

-- Trigger: log salary changes
CREATE TRIGGER log_salary_change
AFTER UPDATE ON employees
FOR EACH ROW
BEGIN
    INSERT INTO salary_audit(emp_id, old_salary, new_salary, changed_at)
    VALUES (OLD.id, OLD.salary, NEW.salary, NOW());
END;

Types:

• BEFORE / AFTER triggers
• ROW-level / Statement-level triggers

Use cases: Audit logging, enforcing business rules, auto-updating derived columns, cascading changes.

Q33. ⭐ What is a stored procedure? How is it different from a function?

Answer: