Longest Consecutive Sequence

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.

 

Example 1:

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.

Example 2:

Input: nums = [0,3,7,2,5,8,4,6,0,1]
Output: 9

 

Constraints:

• 0 <= nums.length <= 105
• -109 <= nums[i] <= 109

Solution(javascript)

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