[leetcode]Maximum Product Subarray

DP.类似最大和。就是要记录正的和负的两种情况。

class Solution {

public:

    int maxProduct(int A[], int n) {

        vector<int> positive(n);

        vector<int> minus(n);

        int result = A[0];

        for (int i = 0; i < n; i++) {

            int minVal = A[i];

            int maxVal = A[i];

            if (i > 0) {

                minVal = min(minVal, positive[i - 1] * A[i]);

                minVal = min(minVal, minus[i - 1] * A[i]);

                maxVal = max(maxVal, positive[i - 1] * A[i]);

                maxVal = max(maxVal, minus[i - 1] * A[i]);

            }

            positive[i] = maxVal > 0 ? maxVal : 1;

            minus[i] = minVal < 0 ? minVal : 1;

            result = max(result, maxVal);

        }

        return result;

    }

};