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];

    }

};