72Laboratories

📚 Frequently Asked Coding Questions (Fresher’s CheatSheet)

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🔢 Arrays

🟢 Basic Logic-Based Questions

1. Find the Sum of All Elements in an Array

• Task: Calculate the sum of all elements.
• Example: Input: [1, 2, 3, 4, 5] → Output: 15
• Approach: Iterate through the array, adding each element to a running total.
• Time Complexity: O(n)

2. Find the Maximum and Minimum Element in an Array

• Task: Identify the largest and smallest elements.
• Example: Input: [3, 5, 2, 9, 1] → Output: Max = 9, Min = 1
• Approach: Track max and min while iterating.
• Time Complexity: O(n)

3. Calculate the Average of Elements in an Array

• Task: Compute the average of all elements.
• Example: Input: [1, 2, 3, 4, 5] → Output: 3
• Approach: Sum all elements and divide by length.
• Time Complexity: O(n)

4. Search for a Specific Element in an Array (Linear Search)

• Task: Find index of first occurrence or return -1.
• Example: Input: [10, 20, 30, 20, 40], target = 20 → Output: 1
• Time Complexity: O(n)

5. Count the Number of Even and Odd Numbers in an Array

• Task: Count even and odd numbers.
• Example: Input: [1, 2, 3, 4, 5, 6] → Output: Even: 3, Odd: 3
• Time Complexity: O(n)

6. Find the Second Largest Element in an Array

• Task: Identify second-highest element.
• Example: Input: [5, 2, 9, 1, 5] → Output: 5
• Time Complexity: O(n)

7. Reverse an Array In-Place

• Task: Reverse without using extra space.
• Example: Input: [1, 2, 3, 4] → Output: [4, 3, 2, 1]
• Time Complexity: O(n)

8. Copy One Array into Another

• Task: Create a new array with the same elements.
• Example: Input: [1, 2, 3] → Output: [1, 2, 3]
• Time Complexity: O(n)

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🟡 Slightly Interesting / Tricky Questions

9. Find Duplicate Elements in an Array

• Example: Input: [1, 2, 2, 3, 4, 4, 5] → Output: [2, 4]
• Time Complexity: O(n)

10. Remove Duplicates from a Sorted Array In-Place

• Example: Input: [1, 1, 2, 2, 3] → Output: [1, 2, 3] (length = 3)
• Time Complexity: O(n)

11. Sort an Array (Ascending and Descending)

• Example: Input: [5, 2, 8, 1] → Asc: [1, 2, 5, 8], Desc: [8, 5, 2, 1]
• Time Complexity: O(n²)

12. Merge Two Sorted Arrays

• Example: [1, 3, 5], [2, 4, 6] → Output: [1, 2, 3, 4, 5, 6]
• Time Complexity: O(n + m)

13. Left and Right Rotate an Array by One Position

• Example: [1, 2, 3, 4, 5] → Left: [2, 3, 4, 5, 1], Right: [5, 1, 2, 3, 4]
• Time Complexity: O(n)

14. Rotate an Array by k Positions

• Example: [1, 2, 3, 4, 5], k = 2 → Output: [4, 5, 1, 2, 3]
• Time Complexity: O(n)

15. Find the Frequency of Each Element

• Example: [1, 2, 2, 3] → Output: 1:1, 2:2, 3:1
• Time Complexity: O(n)

16. Move All Zeros to the End

• Example: [1, 0, 2, 0, 3] → Output: [1, 2, 3, 0, 0]
• Time Complexity: O(n)

17. Find the Missing Number

• Example: [1, 2, 4, 5] → Output: 3
• Time Complexity: O(n)

18. Find a Pair with a Given Sum (Two Sum)

• Example: [2, 7, 11, 15], target = 9 → Output: [0, 1]
• Time Complexity: O(n) (hash map)

19. Sort an Array of 0s, 1s, and 2s (Dutch National Flag)

• Example: [2, 0, 1, 2, 1] → Output: [0, 1, 1, 2, 2]
• Time Complexity: O(n)

20. Check if an Array is Sorted in Ascending Order

• Example: [1, 2, 3, 4] → Output: True; [1, 3, 2, 4] → Output: False
• Time Complexity: O(n)

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🎁 Bonus Challenges

21. Check if an Array is a Palindrome

• Example: [1, 2, 2, 1] → Output: True
• Time Complexity: O(n)

22. Find Common Elements Between Two Arrays

• Example: [1, 2, 3], [2, 3, 4] → Output: [2, 3]
• Time Complexity: O(n + m)

23. Difference Between Sum of Even and Odd Numbers

• Example: [1, 2, 3, 4] → Output: |6 - 4| = 2
• Time Complexity: O(n)

24. Product of Array Except Self

• Example: [1, 2, 3, 4] → Output: [24, 12, 8, 6]
• Time Complexity: O(n)

25. Maximum Subarray Sum (Kadane’s Algorithm)

• Example: [-2, 1, -3, 4, -1, 2, 1, -5, 4] → Output: 6
• Time Complexity: O(n)

26. Find the Duplicate Number

• Example: [3, 1, 3, 4, 2] → Output: 3
• Time Complexity: O(n)

27. Container With Most Water

• Example: [1,8,6,2,5,4,8,3,7] → Output: 49
• Time Complexity: O(n)

28. Majority Element

• Example: [2,2,1,1,1,2,2] → Output: 2
• Time Complexity: O(n)

29. Best Time to Buy and Sell Stock

• Example: [7,1,5,3,6,4] → Output: 5
• Time Complexity: O(n)

30. Plus One

• Example: [1, 2, 9] → Output: [1, 3, 0]
• Time Complexity: O(n)

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🧵 String Questions

🟢 Basic Level

• Reverse a String
• Check if a String is a Palindrome
• Count Vowels and Consonants in a String
• Convert String to Uppercase / Lowercase
• Find Duplicate Characters in a String
• Count the Occurrences of a Character in a String
• Remove All White Spaces from a String

🟡 Intermediate Level

• Check if Two Strings are Anagrams
• Remove All Duplicate Characters from a String
• Find the First Non-Repeated Character in a String
• Check if a String Contains Only Digits
• Count the Number of Words in a String
• Find All Substrings of a String
• Find All Subsequences of a String
• Left Rotate a String by d Positions
• Convert String to Integer (atoi)
• Convert Integer to String

🔴 Advanced / Tricky Level

• Print All Permutations of a String
• Check if a String is a Rotation of Another String
• Longest Palindromic Substring
• Implement a Basic String Compression
• Find the Longest Common Prefix among a Set of Strings
• Group Anagrams
• Implement Regular Expression Matching (basic cases like . and *)
• Find the Longest Substring Without Repeating Characters

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✖️➕🟰 Math-Based Questions

🟢 Basic Level

1. Check if a Number is Prime
2. Generate First N Prime Numbers
3. Check if a Number is Palindrome
4. Reverse a Number
5. Check if a Number is an Armstrong Number
6. Calculate the Factorial of a Number
7. Print All Factors of a Number
8. Find the Greatest Common Divisor (GCD)
9. Find the Least Common Multiple (LCM)
10. Count Digits in a Number
11. Sum of Digits in a Number
12. Check if a Number is a Perfect Square
13. Check if a Number is a Power of Two
14. Convert Decimal to Binary
15. Convert Binary to Decimal

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🟡 Intermediate Level

1. Generate the Fibonacci Sequence up to N Terms
2. Find the Nth Fibonacci Number
3. Find the Integer Square Root of a Number
4. Calculate the Power of a Number (Exponentiation)
5. Count the Number of Set Bits (1s) in Binary
6. Check if a Number is a Power of 10
7. Compute nCr (Combinations)
8. Check for Leap Year
9. Find the Number of Trailing Zeros in Factorial
10. Implement Arithmetic Operations Without Using Operators (Add, Subtract, Multiply, Divide)
11. Check Whether Three Numbers Can Form a Triangle

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🔴 Advanced Level

1. Sieve of Eratosthenes (Generate Primes up to n)
2. Find All Prime Factors of a Number
3. Convert Roman Numerals to Integer
4. Check if a Number Has All Unique Digits (No Repetition)
5. Missing Number in a Sequence (1 to n)
6. Two Sum Problem (Find Pair with Given Sum)
7. Generate Pascal’s Triangle (n Rows)
8. Find the Digital Root of a Number
9. Find Modular Multiplicative Inverse
10. Fast Exponentiation (Modular Power)