Interview Q&A / Data Structures & Algorithms

1. How do you merge two sorted arrays into one sorted array?

   Use two pointers, one at the start of each array. Compare the two current elements, copy the smaller one to the result and move that pointer forward. When one array runs out, copy the rest of the other. This is O(n + m) time, much better than joining and sorting again.

   BeginnerIn-depthCoding3 min read
2. Two Sum - find two numbers that add up to a target

   Walk through the array once and store each number's index in a hash map. For each number, check if target minus that number is already in the map. This takes O(n) time.

   BeginnerIn-depthCoding2 min read
3. How do you check if a string is a palindrome, ignoring spaces, punctuation and case?

   Use two pointers from both ends. Skip characters that are not letters or digits, compare the rest in lowercase, and move inward. If any pair differs, it is not a palindrome.

   BeginnerQuick answerCoding1 min read
4. How do you find the middle node of a linked list in one pass?

   Use two pointers: slow moves one step, fast moves two. When fast reaches the end, slow is at the middle. For an even length it lands on the second of the two middle nodes.

   BeginnerQuick answerCoding1 min read
5. How do you remove duplicates from a sorted array in place and return the new length?

   Keep a write index. Because the array is sorted, a value is new only if it differs from the last value written. Copy it forward and advance the write index; the final write index is the new length.

   BeginnerQuick answerCoding1 min read
6. Write a function that moves all zeroes to the end of an array while keeping the order of the other elements.

   Use a write pointer: copy every non-zero value forward to the write position, then fill the remaining slots with zeroes. One pass, no extra array.

   BeginnerQuick answerCoding1 min read