[Leetcode]128. Longest Consecutive Sequence

題目 : 128. Longest Consecutive Sequence Medium

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

1.

numSet : 用set()函數將nums做成集合，去除重複的數字

longest : 紀錄目前最大長度

length : 記錄由num開始算連續數字的長度

line 8 : 先看num是不是連續整數中的最小數，如果是就開始往後找num+1、num+2....

直到找到連續整數的最大長度

line 12 : 跳出迴圈後查看紀錄的length和longest那個最大，用max()回傳最大長度

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

        for num in nums :
            if num-1 not in numSet:
                length = 0
                while (num+length) in numSet:
                    length += 1
                longest = max(length,longest)

        return longest