Interview Q&A / Data Structures & Algorithms

1. 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
2. How do you check whether two strings are anagrams of each other?

   Two strings are anagrams if they have the same letters with the same counts. Count the characters of the first string, subtract using the second, and check that every count ends at zero.

   BeginnerQuick answerCoding1 min read
3. How do you find the first non-repeating character in a string?

   Count how often each character appears in one pass, then scan again and return the first character whose count is 1.

   BeginnerQuick answerCoding1 min read
4. How does a hash map handle collisions?

   A collision happens when two keys hash to the same bucket. Chaining stores colliding entries in a list inside the bucket; open addressing probes for the next free slot. Both keep lookups near O(1) on average if the table stays sparse.

   BeginnerQuick answer1 min read
5. When should you use a Map instead of a plain object in JavaScript?

   Use a Map when keys are not just strings, when you add and remove entries often, or when you need a reliable size and insertion order. Use a plain object for fixed, string-keyed records.

   BeginnerQuick answer1 min read