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
Explanation: The longest consecutive elements sequence is [0, 1, 2, 3, 4, 5, 6, 7, 8]. Therefore its length is 9.
Example 3:
Input: nums = [1,0,-1]
Output: 3
Explanation: The longest consecutive elements sequence is [-1, 0, 1]. Therefore its length is 3.
0 <= nums.length <= 10^5-10^9 <= nums[i] <= 10^9