leetcode/work/1/Medium/Array/128.longest-consecutive-sequence.py

"""
128. Longest Consecutive Sequence
Difficulty: Medium
https://leetcode.com/problems/longest-consecutive-sequence/

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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

Example 3:

Input: nums = [1,0,1,2]
Output: 3



Constraints:

        • 0 <= nums.length <= 10^5

        • -10^9 <= nums[i] <= 10^9
"""


class Solution:
    def longestConsecutive(self, nums: list[int]) -> int:
        seen = set(nums)
        best = 0

        for n in seen:
            if n - 1 in seen:
                continue

            length = 1
            while length + n in seen:
                length += 1

            best = max(length, best)

        return best