[Oracle] LeetCode 41 First Missing Positive 思维

Given an unsorted integer array nums, return the smallest missing positive integer.

You must implement an algorithm that runs in $O(n)$ time and uses constant extra space.

Solution

对于 $nums[i]$ 它对应的位置应该是 $nums[nums[i]-1]$

点击查看代码

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        int n = nums.size();
        for(int i=0;i<n;i++){
            while(nums[i]>0&& nums[i]<=n && nums[i]!=nums[nums[i]-1])swap(nums[i], nums[nums[i]-1]);
        }
        for(int i=0;i<n;i++)
            if(nums[i]!=i+1)return i+1;
        return n+1;
    }
};