152. 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; //注意这里要保存curMax原来的值，因为下面一行代码将会改变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;
}
};