{"id":4773,"date":"2025-03-13T14:32:10","date_gmt":"2025-03-13T14:32:10","guid":{"rendered":"https:\/\/www.kaashivinfotech.com\/blog\/?p=4773"},"modified":"2025-07-18T08:32:06","modified_gmt":"2025-07-18T08:32:06","slug":"100-coding-interview-questions-and-answers","status":"publish","type":"post","link":"https:\/\/www.kaashivinfotech.com\/blog\/100-coding-interview-questions-and-answers\/","title":{"rendered":"100+ Essential Coding Interview Questions to Ace Your Next Tech Interview [Updated]"},"content":{"rendered":"

Feeling Stressed About Coding Interviews? You\u2019re Not Alone!<\/strong><\/h2>\n

Let\u2019s be real\u2014coding interview questions<\/strong> can be nerve-wracking. The pressure, the whiteboard coding, the algorithm-heavy challenges\u2026it\u2019s enough to make anyone break a sweat. I\u2019ve been there. You spend weeks grinding LeetCode, watching YouTube tutorials, and still feel unprepared when the big day arrives. Sound familiar?<\/p>\n

That\u2019s exactly why I created this ultimate list of 100+ essential coding interview questions<\/a><\/strong>\u2014so you don\u2019t waste time on random problems that might not even matter. These common coding interview questions<\/a><\/strong> cover everything: arrays, linked lists, trees, dynamic programming, and even system design\u2014everything tech companies love to ask.<\/p>\n

Whether you\u2019re a seasoned candidate or just starting out, these coding interview questions for freshers<\/strong> will help you build a strong foundation and develop confidence.<\/p>\n

Let\u2019s dive in and take the stress out of your prep.<\/p>\n

100+ Essential Coding Interview Questions<\/strong><\/h2>\n
\"Coding
100+ Essential Coding Interview Questions<\/figcaption><\/figure>\n

Array-Based Coding Interview Questions for Freshers<\/strong><\/h2>\n
    \n
  1. How do you find the missing number in an array from 1 to n?<\/strong> Use the formula sum = n*(n+1)\/2. Subtract actual array sum from it to get the missing number. Time complexity is O(n).<\/li>\n
  2. How do you find the duplicate number in an array?<\/strong> Use Floyd\u2019s Tortoise and Hare (Cycle Detection) algorithm for efficient results. Time complexity is O(n), space O(1).<\/li>\n
  3. How do you rotate an array by k positions?<\/strong> Reverse the whole array, reverse first k and then reverse the rest. Time complexity is O(n), space O(1).<\/li>\n
  4. How do you find the maximum subarray sum?<\/strong> Use Kadane\u2019s Algorithm. Maintain a current max and update global max accordingly.<\/li>\n
  5. How do you merge two sorted arrays?<\/strong> Use two pointers to merge them into a third array. Time complexity is O(n + m).<\/li>\n
  6. Find the intersection of two arrays.<\/strong> Use a HashSet to store one array, then check the second. Time complexity is O(n).<\/li>\n
  7. How do you sort an array of 0s, 1s, and 2s?<\/strong> Use the Dutch National Flag algorithm. It runs in O(n) time.<\/li>\n
  8. Find the leader elements in an array.<\/strong> Traverse from the right, track max so far. Elements greater than all to their right are leaders.<\/li>\n
  9. How do you find the majority element in an array?<\/strong> Use Moore’s Voting Algorithm. Time complexity O(n), space O(1).<\/li>\n
  10. How do you rearrange array elements in alternating positive and negative items?<\/strong> Partition the array, then swap alternately. Time complexity is O(n).<\/li>\n<\/ol>\n

    String-Based Coding Interview Questions for Freshers<\/strong><\/h2>\n
      \n
    1. Check if a string is a palindrome.<\/strong> Use two pointers from start and end. Compare characters until middle.<\/li>\n
    2. Find the first non-repeating character in a string.<\/strong> Use a frequency counter, then iterate again to find the first. Time complexity is O(n).<\/li>\n
    3. Reverse a string without affecting special characters.<\/strong> Use two-pointer technique while skipping non-alphabetic. Swap only letters.<\/li>\n
    4. Check if two strings are anagrams.<\/strong> Sort and compare or use frequency arrays. Time complexity is O(n log n) or O(n).<\/li>\n
    5. Implement strstr (substring search).<\/strong> Use the KMP algorithm for efficient matching. Time complexity is O(n + m).<\/li>\n
    6. Find the longest common prefix.<\/strong> Sort and compare first and last strings. Check character by character.<\/li>\n
    7. Find the longest palindrome substring.<\/strong> Use dynamic programming or center expansion. Time complexity is O(n^2).<\/li>\n
    8. How do you compress a string (aabcc becomes a2b1c2)?<\/strong> Iterate and count consecutive characters. Concatenate character and count.<\/li>\n
    9. Check if string has all unique characters.<\/strong> Use a set or boolean array. Time complexity is O(n).<\/li>\n
    10. Remove duplicate characters in a string.<\/strong> Use a set to track seen characters. Build a new string skipping duplicates.<\/li>\n<\/ol>\n

      Linked List Coding Interview Questions for Freshers<\/strong><\/h2>\n
        \n
      1. Detect a loop in a linked list.<\/strong> Use Floyd\u2019s cycle detection algorithm. Tortoise and hare pointer method.<\/li>\n
      2. Find the middle element of a linked list.<\/strong> Use slow and fast pointer. Slow will be at middle when fast reaches end.<\/li>\n
      3. Reverse a linked list.<\/strong> Iteratively change next pointers. Use three pointers: prev, curr, next.<\/li>\n
      4. Check if a linked list is a palindrome.<\/strong> Find middle, reverse second half, compare halves. Time complexity is O(n).<\/li>\n
      5. Merge two sorted linked lists.<\/strong> Use a dummy node and iterate. Compare node values and attach accordingly.<\/li>\n<\/ol>\n

        Tree-Based Coding Interview Questions for Freshers<\/h2>\n
          \n
        1. What is the height of a binary tree?<\/strong> Recursively find the height of left and right subtrees. Return max height + 1.<\/li>\n
        2. Check if two trees are identical.<\/strong> Recursively check if both roots, left, and right match. Base case is when both nodes are null.<\/li>\n
        3. Print in-order traversal of a binary tree.<\/strong> Use recursion: Left -> Root -> Right. You can also use a stack for iterative approach.<\/li>\n
        4. Check if a binary tree is a BST.<\/strong> Use recursion with valid range limits. Ensure left < root < right.<\/li>\n
        5. Find lowest common ancestor in BST.<\/strong> Use recursion based on value comparison. If root lies between two nodes, it’s LCA.<\/li>\n<\/ol>\n

          Recursion-Based Coding Interview Questions for Freshers<\/h2>\n
            \n
          1. Find factorial using recursion.<\/strong> Base case is 1. Return n * factorial(n-1). Time complexity is O(n).<\/li>\n
          2. Generate Fibonacci series using recursion.<\/strong> Return fib(n-1) + fib(n-2) with base cases. Inefficient; better with memoization.<\/li>\n
          3. Reverse a string using recursion.<\/strong> Base case is empty string. Return reverse(substring) + first character.<\/li>\n
          4. Check if a number is a power of 2.<\/strong> Recursively divide by 2 and check if equals 1. Base case is 1.<\/li>\n
          5. Find GCD using recursion.<\/strong> Use Euclidean algorithm: gcd(a, b) = gcd(b, a % b). Base case is when b == 0.<\/li>\n<\/ol>\n

            Sorting and Searching Coding Interview Questions for Freshers<\/h2>\n
              \n
            1. Implement binary search.<\/strong> Compare mid element with target. Use divide-and-conquer on sorted array.<\/li>\n
            2. Implement bubble sort.<\/strong> Swap adjacent elements if out of order. Time complexity is O(n^2).<\/li>\n
            3. Implement insertion sort.<\/strong> Insert elements in sorted position one by one. Best case O(n), worst case O(n^2).<\/li>\n
            4. Implement quick sort.<\/strong> Choose pivot, partition array, and sort recursively. Average case is O(n log n).<\/li>\n
            5. Implement merge sort.<\/strong> Divide array into halves, sort and merge them. Time complexity is O(n log n).<\/li>\n<\/ol>\n

              Graph-Based Coding Interview Questions for Freshers<\/h2>\n
                \n
              1. Implement depth-first search (DFS).<\/strong> Use stack or recursion to visit nodes. Mark nodes as visited to avoid cycles.<\/li>\n
              2. Implement breadth-first search (BFS).<\/strong> Use queue to explore neighbors layer by layer. Track visited nodes to prevent repetition.<\/li>\n
              3. Detect a cycle in an undirected graph.<\/strong> Use DFS and track parent of each node. Cycle exists if a visited node is not parent.<\/li>\n
              4. Detect a cycle in a directed graph.<\/strong> Use DFS with recursion stack. Back edge indicates a cycle.<\/li>\n
              5. Topological sort of a DAG.<\/strong> Use DFS or Kahn\u2019s Algorithm. Order tasks with no cyclic dependencies.<\/li>\n<\/ol>\n

                Stack and Queue Coding Interview Questions for Freshers<\/h2>\n
                  \n
                1. Implement a stack using two queues.<\/strong> Push to one queue, pop by transferring to other. Maintain latest element at front.<\/li>\n
                2. Implement a queue using two stacks.<\/strong> Push to one stack, pop by reversing to other. Use amortized O(1) operations.<\/li>\n
                3. Check for balanced parentheses.<\/strong> Use stack to track opening brackets. Match with closing ones.<\/li>\n
                4. Evaluate a postfix expression.<\/strong> Use stack to store operands. Apply operators as encountered.<\/li>\n
                5. Implement LRU cache.<\/strong> Use HashMap and Doubly Linked List. Maintain order of usage.<\/li>\n<\/ol>\n

                  Dynamic Programming Coding Interview Questions for Freshers<\/h2>\n
                    \n
                  1. Find nth Fibonacci number using DP.<\/strong> Use memoization or bottom-up approach. Time complexity is O(n).<\/li>\n
                  2. 0\/1 Knapsack Problem.<\/strong> Use DP table to choose max value within capacity. Time complexity is O(nW).<\/li>\n
                  3. Longest common subsequence.<\/strong> Fill DP table based on character match. Result is in last cell.<\/li>\n
                  4. Longest increasing subsequence.<\/strong> Use DP to track increasing order. Update max for each element.<\/li>\n
                  5. Minimum edit distance between two strings.<\/strong> Use DP to calculate insert, delete, replace. Choose min of all operations.<\/li>\n<\/ol>\n

                    Object-Oriented Programming Coding Interview Questions for Freshers<\/h2>\n
                      \n
                    1. What is encapsulation in OOP?<\/strong> Binding data and methods together. Achieved using classes and access modifiers.<\/li>\n
                    2. What is inheritance in OOP?<\/strong> One class acquires properties of another. Supports code reusability.<\/li>\n
                    3. What is polymorphism in OOP?<\/strong> Same function behaves differently in contexts. Overloading and overriding are types.<\/li>\n
                    4. What is abstraction in OOP?<\/strong> Hides internal details, shows essential features. Done using abstract classes or interfaces.<\/li>\n
                    5. Difference between interface and abstract class?<\/strong> Interfaces have only abstract methods (till Java 7). Abstract class can have concrete methods too.<\/li>\n<\/ol>\n

                      Bit Manipulation Coding Interview Questions<\/strong><\/h2>\n
                        \n
                      1. Check if a number is a power of two.<\/strong>
                        \nUse n & (n – 1) to check. If result is 0 and n > 0, it’s a power of two.<\/li>\n
                      2. Count set bits in an integer.<\/strong>
                        \nUse Brian Kernighan\u2019s algorithm. Subtract 1 and AND it with the original number until 0.<\/li>\n
                      3. Find the only non-repeating element.<\/strong>
                        \nUse XOR across all numbers. Duplicate elements cancel out.<\/li>\n
                      4. Add two numbers without using ‘+’ operator.<\/strong>
                        \nUse bitwise XOR for addition and AND + shift for carry. Repeat until carry is zero.<\/li>\n
                      5. Swap two numbers using bitwise operators.<\/strong>
                        \nUse XOR: a = a ^ b, b = a ^ b, a = a ^ b.<\/li>\n
                      6. Find position of rightmost set bit.<\/strong>
                        \nUse n & -n. This isolates the rightmost set bit in binary.<\/li>\n<\/ol>\n

                        Greedy Algorithm Coding Interview Questions<\/strong><\/h2>\n
                          \n
                        1. Activity selection problem.<\/strong>
                          \nSort by end time and choose non-overlapping intervals. Maximizes task completion.<\/li>\n
                        2. Minimum number of platforms required for trains.<\/strong>
                          \nSort arrival and departure separately, and simulate overlapping.<\/li>\n
                        3. Fractional Knapsack Problem.<\/strong>
                          \nSort by value\/weight ratio. Take max possible items greedily.<\/li>\n
                        4. Job Sequencing Problem.<\/strong>
                          \nSort by profit and fill time slots greedily to maximize gain.<\/li>\n
                        5. Huffman Coding.<\/strong>
                          \nUse priority queue to build optimal prefix tree for encoding.<\/li>\n
                        6. Minimum number of coins.<\/strong>
                          \nUse highest denomination coins first (greedy) to reach the total amount.<\/li>\n<\/ol>\n

                          Math and Logic Puzzle Coding Interview Questions<\/strong><\/h2>\n
                            \n
                          1. Check if a number is prime.<\/strong>
                            \nCheck divisibility from 2 to \u221an. Return false if divisible.<\/li>\n
                          2. Find GCD of two numbers.<\/strong>
                            \nUse Euclidean algorithm: gcd(a, b) = gcd(b, a % b).<\/li>\n
                          3. Check if a number is palindrome.<\/strong>
                            \nReverse the number and compare with original.<\/li>\n
                          4. Find square root without library.<\/strong>
                            \nUse binary search between 1 and n.<\/li>\n
                          5. Check if number is an Armstrong number.<\/strong>
                            \nSum of each digit raised to power of total digits equals number.<\/li>\n
                          6. FizzBuzz problem.<\/strong>
                            \nPrint “Fizz” for multiples of 3, “Buzz” for 5, and “FizzBuzz” for both.<\/li>\n<\/ol>\n

                            Common Coding Interview Questions<\/strong><\/h2>\n
                              \n
                            1. Reverse an integer.<\/strong>
                              \nExtract digits and construct reversed number. Handle overflows.<\/li>\n
                            2. Convert integer to Roman numeral.<\/strong>
                              \nMap integer values to Roman symbols. Greedily subtract values.<\/li>\n
                            3. Convert Roman numeral to integer.<\/strong>
                              \nAdd or subtract values based on symbol position.<\/li>\n
                            4. Excel sheet column number to title.<\/strong>
                              \nConvert to base-26 and map to alphabet.<\/li>\n
                            5. Find majority element.<\/strong>
                              \nUse Boyer-Moore voting algorithm for O(n) time.<\/li>\n
                            6. Find longest common prefix among strings.<\/strong>
                              \nUse horizontal scanning or sort then compare first & last.<\/li>\n
                            7. Implement atoi function.<\/strong>
                              \nTrim spaces, handle signs, and parse numbers character by character.<\/li>\n
                            8. Implement strstr function.<\/strong>
                              \nUse two pointers or KMP algorithm for substring search.<\/li>\n
                            9. Implement pow(x, n).<\/strong>
                              \nUse recursion or iterative fast exponentiation with log(n) complexity.<\/li>\n
                            10. Find missing number in 0 to n.<\/strong>
                              \nSum from 0 to n minus sum of array gives missing number.<\/li>\n
                            11. Find duplicate number in array.<\/strong>
                              \nUse Floyd\u2019s cycle detection algorithm or visited index marking.<\/li>\n
                            12. Detect cycle in an array.<\/strong>
                              \nFloyd’s cycle detection technique using slow and fast pointers.<\/li>\n
                            13. Find kth largest element.<\/strong>
                              \nUse heap or quickselect for average O(n) time.<\/li>\n
                            14. Longest consecutive sequence.<\/strong>
                              \nUse HashSet and check sequence starts with n-1 not existing.<\/li>\n
                            15. Count primes less than n.<\/strong>
                              \nUse Sieve of Eratosthenes for efficient counting.<\/li>\n
                            16. Valid Parentheses.<\/strong>
                              \nUse stack to push on opening and pop on matching closing.<\/li>\n
                            17. Group Anagrams.<\/strong>
                              \nSort each string or use character frequency map as key in HashMap.<\/li>\n
                            18. Top K Frequent Elements.<\/strong>
                              \nUse HashMap for count and Min Heap or Bucket Sort to find top k.<\/li>\n
                            19. Isomorphic Strings.<\/strong>
                              \nMap characters from s to t and ensure consistent mapping.<\/li>\n
                            20. Minimum Window Substring.<\/strong>
                              \nUse sliding window with frequency count comparison.<\/li>\n
                            21. Decode Ways.<\/strong>
                              \nUse DP: ways[i] = ways[i-1] + ways[i-2] depending on digits.<\/li>\n
                            22. Find First and Last Position of Element in Sorted Array.<\/strong>
                              \nUse binary search twice for left and right bounds.<\/li>\n
                            23. Search in Rotated Sorted Array.<\/strong>
                              \nUse modified binary search with pivot consideration.<\/li>\n
                            24. Median of Two Sorted Arrays.<\/strong>
                              \nUse binary search partitioning technique. Complex but optimal.<\/li>\n
                            25. Wildcard Matching.<\/strong>
                              \nUse DP or greedy two-pointer technique with backtracking.<\/li>\n
                            26. Regular Expression Matching.<\/strong>
                              \nUse recursion or DP to match ‘.’ and ‘*’ patterns.<\/li>\n
                            27. Implement LRU Cache.<\/strong>
                              \nUse HashMap with Doubly Linked List for O(1) operations.<\/li>\n
                            28. Serialize and Deserialize Binary Tree.<\/strong>
                              \nUse BFS or DFS with delimiters for nulls.<\/li>\n
                            29. Sliding Window Maximum.<\/strong>
                              \nUse deque to maintain decreasing order of values within window.<\/li>\n
                            30. Trapping Rain Water.<\/strong>
                              \nUse two-pointer technique or precompute left\/right max arrays.<\/li>\n
                            31. Word Ladder.<\/strong>
                              \nUse BFS to transform word by changing one letter at a time.<\/li>\n
                            32. Alien Dictionary (Topological Sort).<\/strong>
                              \nBuild graph from character orders and apply Kahn\u2019s algorithm.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

                              Feeling Stressed About Coding Interviews? You\u2019re Not Alone! Let\u2019s be real\u2014coding interview questions can be nerve-wracking. The pressure, the whiteboard coding, the algorithm-heavy challenges\u2026it\u2019s enough to make anyone break a sweat. I\u2019ve been there. You spend weeks grinding LeetCode, watching YouTube tutorials, and still feel unprepared when the big day arrives. Sound familiar? That\u2019s exactly […]<\/p>\n","protected":false},"author":3,"featured_media":8525,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[724],"tags":[3414,3409,3403,3410,3418,3406,3405,3415,3413,3417,3404,3416,3407,3411,3419,767,770,3408,3412,3420],"class_list":["post-4773","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-interview-questions","tag-angular-coding-interview-questions","tag-c-coding-interview-questions","tag-coding-interview-questions","tag-coding-interview-questions-with-solutions","tag-google-coding-interview-questions","tag-java-8-coding-interview-questions","tag-java-coding-interview-questions","tag-java-coding-interview-questions-and-answers","tag-java-coding-interview-questions-for-5-years-experience","tag-java-coding-interview-questions-for-freshers","tag-javascript-coding-interview-questions","tag-js-coding-interview-questions","tag-medical-coding-interview-questions","tag-medical-coding-interview-questions-for-freshers","tag-pyspark-coding-interview-questions","tag-python-coding-interview-questions","tag-python-coding-interview-questions-and-answers","tag-react-coding-interview-questions","tag-sql-coding-interview-questions","tag-stream-api-coding-interview-questions"],"_links":{"self":[{"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/posts\/4773","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/comments?post=4773"}],"version-history":[{"count":0,"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/posts\/4773\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/media\/8525"}],"wp:attachment":[{"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/media?parent=4773"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/categories?post=4773"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.kaashivinfotech.com\/blog\/wp-json\/wp\/v2\/tags?post=4773"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}