[Leetcode] 0128. Longest Consecutive Sequence

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內容目錄

Medium

 

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

Python

				
					from typing import List


class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        longestStreak = 0
        numSet = set(nums)

        for num in nums:
            if num - 1 not in numSet:
                currentNum = num
                currentStreak = 1

                while currentNum + 1 in numSet:
                    currentNum += 1
                    currentStreak += 1

                longestStreak = max(longestStreak, currentStreak)

        return longestStreak

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