Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence. Must run in O(n) time.

Example 1:

Input:  100 4 200 1 3 2
Output: 4

(1, 2, 3, 4)

Example 2:

Input:  0 3 7 2 5 8 4 6 0 1
Output: 9

Input format: Space-separated integers.