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Longest Consecutive Sequence

medium
Time: O(n)
Space: O(n)

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.

Constraints

  • 0 <= nums.length <= 10^5
  • -10^9 <= nums[i] <= 10^9

Examples

Input: nums = [100,4,200,1,3,2]
Output: 4
Longest: [1, 2, 3, 4].
Input: nums = [0,3,7,2,5,8,4,6,0,1]
Output: 9