leetcode 41. First Missing Posit

Given an unsorted integer array, find the smallest missing positive integer.

Example 1:

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

Example 2:

Input: [3,4,-1,1]
Output: 2

Example 3:

Input: [7,8,9,11,12]
Output: 1

Note:

Your algorithm should run in O(n) time and uses constant extra space.

class Solution:
    def firstMissingPositive(self, nums: List[int]) -> int:
        i = 1
        while i in nums:
            i += 1
        return i

这题主要是要理解题目在说什么，其实是找最小正整数(默认情况是1)，那我们只要从1开始递增，如果一直在nums中出现，那最后只要比最后在nums中出现的正整数大1就可以了

还有就是while i in nums等效于

while True:
    if i in nums:
        dosomething
    else:
        break

一般不会这么写，但在这里这样写还算比较容易理解