41. First Missing Positive(C++)

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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.

 

Solution:

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

　　

41. First Missing Positive(C++)