#128 - Longest Consecutive Sequence

Medium • View on LeetCode • View on GitHub

Problem Description

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.

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var longestConsecutive = function(nums) {
  const set = new Set(nums);
  let result = 0;

  for (const num of set) {
    if (!set.has(num - 1)) {
      let count = 1;
      let n = num;

      while (set.has(n + 1)) {
        n++;
        count++;
      }
      result = Math.max(result, count);
    }
  }

  return result;
};