[leetcode] 128. Longest Consecutive Sequence @ python

最长连续序列算法解析

最新推荐文章于 2025-09-25 09:01:15 发布

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本文介绍了一种在未排序整数数组中寻找最长连续元素序列的算法，该算法的时间复杂度为O(n)，通过去除重复值并排序，然后遍历数组以计算最长连续序列的长度。示例输入为[100,4,200,1,3,2]，输出为4，解释为最长连续序列是[1,2,3,4]。

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Your algorithm should run in O(n) complexity.

Example:

Input: [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

解法

先将nums去掉重复值, 再升序排列, 遍历nums, 将计数的值加到结果中, 最后取最大值.
Time: O(n)
Space: O(1)

代码

class Solution:
    def longestConsecutive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        # edge case
        if not nums: return 0        
        nums = sorted(list(set(nums)))
        if len(nums) == 1: 
            return 1         
        count = 1
        ans = [count]
        for i in range(1, len(nums)):
            if nums[i] - nums[i-1] == 1:
                count += 1
                ans.append(count)
            else:
                ans.append(count)
                count = 1
        return max(ans)