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.

这类题目的思路一般都是复用原数组，并且将数组中的元素hash到原数组中，看过陈利仁老师所说的“元神归位法”，这道题目就很简单了。

以下是我的代码：

class Solution{
public:
	int firstMissingPositive(int A[], int n){
		if(A==NULL || n<0) throw "Invalid Arguments!";
		
		if(n==0) return 1;

		int i = 0;

		// Find the smallest num Greater than 0.
		int minNum = INT_MAX;
		for(i=0; i<n; i++){
			if(A[i]<minNum&&A[i]>0){
				minNum = A[i];
			}
		}

		if(minNum>1||minNum<=0){
			return 1;
		}

		// Hash the num using A[i]-minNum.
		for(i=0; i<n; ){
			if((A[i]!=minNum+i)&&
			   (A[i]>0)&&
			   (A[i]<minNum+n)&&
			   (A[A[i]-minNum]!=A[i])){
				swap(A,i,A[i]-minNum);
			}
			else{
				i++;
			}
		}

		for(i=0; i<n; i++){
			if(A[i]!=i+minNum){
				break;
			}
		}

		return (i+minNum);

	}
private:
	void swap(int A[], int i, int j){
		int temp = A[i];
		A[i] = A[j];
		A[j] = temp;
	}
};