public class Solution
extends Object
128 - Longest Consecutive Sequence\.
Medium
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