[LeetCode]First Missing Positive

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

For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.

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

class Solution {public:    int firstMissingPositive(vector<int>& nums) { //交换的方法        int len = nums.size();        for(int i=0; i<len; ++i){            if(nums[i]==i+1)                continue;            while(nums[i]!=i+1&&nums[i]>0&&nums[i]<nums.size()&&nums[i]!=nums[nums[i]-1]){ //交换直到直到出现无效的i位            //注意边界条件，和重复交换的情况                swap(nums[i],nums[nums[i]-1]);            }        }        int i;        for(i=0; i<len; ++i){ //找到第一个不匹配的数字            if(nums[i]!=i+1)                break;        }        return i+1;    }    void swap(int &a,int &b){        int temp = a;        a = b;        b = temp;    }};