First_Missing_Positive.cc

﻿class Solution {
public:
    int firstMissingPositive(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int tmp;
        for (int i = 0; i < n; i++) {
            while (A[i] != i + 1) {
                if (A[i] <= 0 || A[i] > n || A[i] == A[ A[i] - 1 ]) {
                    break;
                }
                swap(A[i], A[ A[i] - 1 ]);
            }
        }
        for (int i = 0; i < n; i++) {
            if (A[i] != i + 1) {
                return i + 1;
            }
        }
        return n + 1;
    }
};