First_Missing_Positive.cpp

class Solution {
public:
	void mySwap(int &a, int &b) {
		int c = a;
		a = b;
		b = c;
	}

    int firstMissingPositive(int A[], int n) {
        for(int i = 0; i < n; ++i) {
        	if(A[i] > 0 && A[i] < n && A[i] != A[A[i]-1]) {
        		mySwap(A[i], A[A[i]-1]);
        		--i;
        	}
        }

        for(int i = 0; i < n; ++i) {
        	if(A[i] != i + 1)
        		return i + 1;
        }

        return n + 1;
    }
};