Interview Q&A / Data Structures & Algorithms

1. How do you find the longest palindromic substring in a string?

   Every palindrome has a centre. Try each index as an odd-length centre and each gap between letters as an even-length centre, expand outward while the ends match, and keep the longest.

   IntermediateQuick answerCoding1 min read
2. How do you generate all valid combinations of n pairs of parentheses?

   Build the string character by character. You may add an opening bracket while fewer than n have been used, and a closing bracket only when it would not exceed the number of openings. A string of length 2n is valid.

   IntermediateQuick answerCoding1 min read
3. How do you group anagrams together from a list of words?

   Anagrams share the same sorted letters, so use the sorted word as a hash map key and collect each word under its key. The map values are the groups.

   IntermediateQuick answerCoding1 min read