LeetCode 53. Maximum Subarray

class Solution {
public:
    int max(int a, int b) {
        return a > b ? a : b;
    }
    int maxSubArray(int A[], int n) {
        int sum = 0;
        int ret = INT_MIN;
        for(int i = 0; i < n; ++i) {
            sum = max(sum + A[i], A[i]);
            ret = max(ret, sum);
        }
        return ret;
    }
};

I want to use subarry sum, but it seems doesn't work....hmm....