LeetCode — Longest consecutive sequence (Blind Curated 31)

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

Solution:

Time complexity: O(N)

Space complexity: O(1)

LC — Longest Consecutive Sequence (Blind Curated 31)