DEV Community

Stylus07
Stylus07

Posted on

Longest Consecutive Sequence

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.

Input: nums = [100,4,200,1,3,2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
Enter fullscreen mode Exit fullscreen mode

var longestConsecutive = function (nums) {
    let num_set = new Set(nums);
    let longestStreak = 0;
    for (let num of nums) {
        if (!num_set.has(num - 1)) {
            let currentNum = num;
            let currentStreak = 1;
            while (num_set.has(currentNum + 1)) {
                currentNum += 1;
                currentStreak += 1;
            }
            longestStreak = Math.max(longestStreak, currentStreak);
        }
    }
    return longestStreak;
}
Enter fullscreen mode Exit fullscreen mode

Time Complexity : O(n)

Top comments (0)