Question 1

1. Reverse a string

Accepted Answer

Reversing a string is a fundamental algorithm. It tests basic string manipulation, array conversions, and loop iteration. While most languages have built-in utilities, knowing the manual pointer or loop approach is essential.

Question 2

2. Check palindrome

Accepted Answer

A palindrome is a string that reads the same forwards and backwards (e.g., 'madam'). The optimal approach uses two pointers starting at opposite ends and moving inward, resulting in O(N/2) time complexity and O(1) space.

Question 3

3. First non-repeating character

Accepted Answer

To find the first unique character, iterate through the string to populate a frequency map (Hash Map or array). Then, iterate through the string a second time and return the first character that has a frequency of 1. Time complexity: O(N).

Question 4

4. Character frequency count

Accepted Answer

Similar to finding the first unique character, calculating character frequencies requires passing over the string and storing the counts in a Hash Map (Dictionary) where the character is the key and the count is the value.

Question 5

5. Remove duplicates from string/array

Accepted Answer

To remove duplicates, the most optimal approach is utilizing a Set data structure, which mathematically prohibits duplicate entries. For preserving original order, you can iterate and add elements to a Set while building a new array/string.

Question 6

6. Check anagram

Accepted Answer

Two strings are anagrams if they contain the exact same characters with the exact same frequencies (e.g., 'listen' and 'silent'). This can be solved by sorting both strings and comparing them, or more optimally in O(N) time using a frequency character map array.

Question 7

7. Bubble sort

Accepted Answer

Bubble sort repeatedly steps through the list, compares adjacent elements, and swaps them if they are in the wrong order. The pass is repeated until the list is sorted. Time complexity is O(N^2), making it highly inefficient for large datasets.

Question 8

8. Selection sort

Accepted Answer

Selection sort divides the array into a sorted and an unsorted region. It repeatedly finds the minimum element from the unsorted region and places it at the end of the sorted region. Time complexity: O(N^2).

Question 9

9. Second largest element

Accepted Answer

To find the second largest element efficiently in a single pass (O(N) time), initialize two variables (largest and second_largest). As you iterate, update these variables whenever a larger value is encountered.

Question 10

10. Missing number (1 to N)

Accepted Answer

The most elegant mathematical approach to finding a missing number in a continuous sequence of 1 to N is using Gauss's Formula: `Sum = (n * (n + 1)) / 2`. Calculate the expected sum, subtract the actual sum of the array, and the difference is the missing number.

Question 11

11. Reverse words in a sentence

Accepted Answer

To reverse the order of words in a sentence (not the characters inside the words), split the string by spaces to get an array of words, reverse the array, and join it back together with spaces.

Question 12

12. Roman ↔ Integer conversion

Accepted Answer

To convert Roman Numerals to Integers, iterate through the string from left to right. If the current numeral represents a smaller value than the next numeral (e.g., 'IV'), subtract its value. Otherwise, add its value to the total.

Question 13

13. Merge sorted arrays

Accepted Answer

To merge two pre-sorted arrays efficiently in O(N + M) time, use the Two-Pointer approach. Maintain an index pointer for both arrays, compare the elements at the pointers, insert the smaller element into a new merged array, and advance the chosen pointer.

Question 14

14. Binary search

Accepted Answer

Binary search is an O(log N) algorithm used to find the position of a target value within a sorted array. It repeatedly divides the search interval in half. If the target is less than the middle element, the search continues in the lower half.

Question 15

15. Longest common prefix

Accepted Answer

To find the longest common prefix string amongst an array of strings, sort the array alphabetically first. The common prefix of the entire array will be strictly limited by the common prefix between the first string and the last string in the sorted array.

Most Asked Programs
in Core Java, Python, JS, TS

1. Reverse a string

2. Check palindrome

3. First non-repeating character

4. Character frequency count

5. Remove duplicates from string/array

6. Check anagram

7. Bubble sort

8. Selection sort

9. Second largest element

10. Missing number (1 to N)

11. Reverse words in a sentence

12. Roman ↔ Integer conversion

13. Merge sorted arrays

14. Binary search

15. Longest common prefix

16. Move zeros to end

17. Rotate array by K steps

18. First repeated character

19. Sort characters by frequency

20. Stack implementation

21. Queue using LinkedList

22. Longest substring without repeating characters

23. Find common elements in arrays

24. Word count in a sentence

25. Digit frequency count

26. Perfect square check

27. Fibonacci series

28. Check balanced brackets

29. GCD of two numbers

30. Factorial using recursion

31. Remove non-alphanumeric characters

32. Convert sentence to title case

Most Asked Programs in Core Java, Python, JS, TS

1. Reverse a string

2. Check palindrome

3. First non-repeating character

4. Character frequency count

5. Remove duplicates from string/array

6. Check anagram

7. Bubble sort

8. Selection sort

9. Second largest element

10. Missing number (1 to N)

11. Reverse words in a sentence

12. Roman ↔ Integer conversion

13. Merge sorted arrays

14. Binary search

15. Longest common prefix

16. Move zeros to end

17. Rotate array by K steps

18. First repeated character

19. Sort characters by frequency

20. Stack implementation

21. Queue using LinkedList

22. Longest substring without repeating characters

23. Find common elements in arrays

24. Word count in a sentence

25. Digit frequency count

26. Perfect square check

27. Fibonacci series

28. Check balanced brackets

29. GCD of two numbers

30. Factorial using recursion

31. Remove non-alphanumeric characters

32. Convert sentence to title case

Most Asked Programs
in Core Java, Python, JS, TS