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;}};