[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.

在原数组A上将数组A中的数进行排序....时间复杂度O(n),空间复杂度O(1)

class Solution {
public:
    int firstMissingPositive(int A[], int n) {
        if(n==0)
            return 1;
        for(int i=0;i<n;i++){
            if(A[i] <= n && A[i]>0 &&  A[i] != i+1){
                if(A[A[i]-1] != A[i]){
                    int tmp = A[A[i]-1];
                    A[A[i]-1] = A[i];
                    A[i] = tmp;
                    i--;
                }
            }
        }//end for
        for(int i=0;i<n;i++){
            if(A[i] != i+1)
                return i+1;
        }
        return n+1;
    }
};