LeetCode 041 First Missing Positive

题目要求：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.

 

代码如下：

class Solution {
public:
    int firstMissingPositive(int A[], int n) {

        for (int i = 0, temp = -1; i < n; i++) {
            while (A[i] - 1 >= 0 && A[i] - 1 < n && A[i] - 1 != i) {
                swap(A, i, A[i] - 1);
                if (A[i] == temp) {
                    break;
                }
                else {
                    temp = A[i];
                }
            }
        }
        for (int i = 0; i < n; i++) {
            if (A[i] - 1 != i) {
                return i + 1;
            }
        }
        return n + 1;
    }

private:
    void swap(int A[], int idx1, int idx2) {
        A[idx1] ^= A[idx2];
        A[idx2] ^= A[idx1];
        A[idx1] ^= A[idx2];
    }
};