[Leetcode] 0128. Longest Consecutive Sequence

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Table of contents

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 sequence of elements 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 <= 10 5
  • -10 9 <= nums[i] <= 10 9

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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