Learn AI Create the Future — with Pranay
Main site

LeetCode solutions

128. Longest Consecutive Sequence

My accepted JavaScript solution to LeetCode problem 128, Longest Consecutive Sequence, running in 34ms.

  • Difficulty: Medium
  • JavaScript
  • Runtime 34ms
  • Memory 81.3MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

JavaScript

Accepted on LeetCode — runtime 34ms, memory 81.3MB, accepted 2025-12-24.

javascript
/**
 * @param {number[]} nums
 * @return {number}
 */
var longestConsecutive = function(nums) {
    const set = new Set(nums);
    let maxLen = 0;
    
    for (const num of set) {
        // Only start counting if num is the start of a sequence
        if (!set.has(num - 1)) {
            let curr = num;
            let len = 1;
            
            while (set.has(curr + 1)) {
                curr++;
                len++;
            }
            
            maxLen = Math.max(maxLen, len);
        }
    }
    
    return maxLen;
};

Source