[LeetCode]First Missing Positive

class Solution {
//first must figure out what is the exactly meaning of this problem
//second hash table is the key
//should practice more
public:
	int firstMissingPositive(int A[], int n) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		for (int i = 0; i < n; ++i)
		{
			if (A[i] > 0 && A[i] < n)
			{
				if (A[i]-1 != i && A[A[i]-1] != A[i])//let A[i] go the right place A[A[i]-1]
				{
					int tmp = A[A[i]-1];
					A[A[i]-1] = A[i];
					A[i] = tmp;
					i--;//the element place where may be wrong
				}
			}
		}
		//check
		for (int i = 0; i < n; ++i)
		{
			if(A[i] != i+1)
				return i+1;
		}
		return n+1;
	}
};

second time

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