#128

Longest Consecutive Sequence

Medium
ArrayHash SetUnion Find

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.

Examples

Example 1
Input: nums = [100,4,200,1,3,2]
Output: 4
The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
Example 2
Input: nums = [0,3,7,2,5,8,1,4,6,0,4]
Output: 9

Constraints

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