LeetCode - 128. Longest Consecutive Sequence

Thoughts:

I choose hash set to solve this problem. This problem need to be done with O(n) time complexity, so do sorting and sliding window is not a good idea (time complexity O(nlogn)). I can find a number, and make sure the number is the start number of a sequence, then, I can try to find the next number in the sequence, and so on… After found all the numbers in a sequence, then compare the current sequence length with the max sequence length until finish the whole sequences I can get.

Code:

/**
 * @param {number[]} nums
 * @return {number}
 */
var longestConsecutive = function (nums) {
  const numsSet = new Set(nums);
  let longest = 0;
  for (let num of nums) {
    if (!numsSet.has(num - 1)) {
      let length = 1;
      while (numsSet.has(num + length)) {
        length++;
      }
      longest = Math.max(length, longest);
    }
  }
  return longest;
};

Reference

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