Leetcode - Longest Consecutive Sequence

Question

Given an unsorted array of integers nums, return _the length of the longest consecutive elements sequence.

You must write an algorithm that runs in O(n) time.

This is an arrays question.

Idea

• We want to turn the list into a set for O(1) indexing
• We iterate for every num in nums
  • Try to find the start of a sequence (does num - 1 exist in the set)
    • If you do find a start, keep count of the longest streak until the sequence runs out (does curr_num + 1 exist?)
    • Update the current number
  • Update the max sequence

Solution