code/train/JavaScript/0004792_leetcode128_LongestConsecutiveSequence.js

// Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

// Your algorithm should run in O(n) complexity.

// Example:

// Input: [100, 4, 200, 1, 3, 2]
// Output: 4
// Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

/**
 * @param {number[]} nums
 * @return {number}
 * score:30.77(80ms)
 * time:O(nlogn)
 * space:O(n)
 */
var longestConsecutive = function (nums) {
    nums = Array.from(new Set(nums));
    if (nums.length < 1) {
        return 0;
    }
    nums.sort((a, b) => a - b);
    let max = 1;
    let cur = 1;
    for (let i = 1; i < nums.length; i++) {
        if (nums[i] - nums[i - 1] === 1) {
            cur++;
        } else {
            if (cur > max) {
                max = cur;
            }
            cur = 1;
        }
    }

    return Math.max(cur, max);
};

/**
 * @param {number[]} nums
 * @return {number}
 * score:94.51(54ms)
 * time:O(n)
 * space:O(n)
 */
var longestConsecutive2 = function (nums) {
    let best = 0;
    let s = new Set(nums);
    for (let i of s) {
        if (!s.has(i - 1)) {
            let cur = i + 1;
            while (s.has(cur)) {
                cur++;
            }
            best = Math.max(best, cur - i);
        }
    }
    return best;
};