喜刷刷: [LeetCode] Maximum Product Subarray

Sunday, November 23, 2014

[LeetCode] Maximum Product Subarray

Find the contiguous subarray within an array (containing at least one number) which has the largest product.

For example, given the array [2,3,-2,4],
the contiguous subarray [2,3] has the largest product = 6.

思路：

Maximum Subarray那题的变种。由于正负得负，负负得正的关系。以A[i]结尾的max product subarray同时取决于以A[i-1]结尾的max / min product subarray以及A[i]本身。因此，对每个i，需要记录min/max product两个状态：

max_product[i] = max(max_product[i-1]*A[i], min_product[i-1]*A[i], A[i])

min_product[i] = min(max_product[i-1]*A[i], min_product[i-1]*A[i], A[i])

class Solution {
public:
    int maxProduct(int A[], int n) {
        if(n<=0) return 0;
        int ret, curMax, curMin;
        ret = curMax = curMin = A[0];
        for(int i=1; i<n; i++) {
            int temp = curMax;
            curMax = max(max(curMax*A[i], curMin*A[i]),A[i]);
            curMin = min(min(temp*A[i], curMin*A[i]),A[i]);
            ret = max(ret, curMax);
        }
        return ret;
    }
};