题解 | #缺失的第一个正整数#

原地哈希，利用下标值作为哈希的一部分

class Solution:
    def minNumberDisappeared(self , nums: List[int]) -> int:
        # write code here
        # 原地哈希
        res = -1
        if not nums:
            return 1
        len_nums = len(nums)
        # 先遍历数组将所有小于0的元素都改成n + 1
        for i in range(len_nums):
            if nums[i] < 0:
                nums[i] = len_nums + 1
        for i in range(len_nums):
            temp = abs(nums[i])
            if temp > 0 and temp <= len_nums:
                nums[temp - 1] = - abs(nums[temp - 1])
        for i in range(len_nums):
            if nums[i] > 0:
                res = i + 1
                break
        if i == len_nums - 1 and res == -1:
            res = len_nums + 1
        return res