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.

题意：找出数组中最大的连续片段乘积。

思路：max(n) = max{ max(n-1), product(...n) }, product是连续乘积到n的最大正值(包含a[n]的连续最大乘积)。所以需记录连续乘积到n-1的最大的正负值。

class Solution {
public:
	int maxProduct(vector<int>& nums) {
		if (nums.size() < 1)
			return 0;
		int maxNum = (numeric_limits<int>::min)();
		int positive = 1;
		int negative = 1;
		for (int i = 0; i < nums.size(); i++){
			if (nums[i] >= 0){
				positive *= nums[i];
				negative *= nums[i];		
			}
			else{
				int tmp = positive;
				positive = negative * nums[i];
				negative = tmp * nums[i];
			}
			if (positive > maxNum)
				maxNum = positive;
			if (positive <= 0)
				positive = 1;
			if (negative >= 0)
				negative = 1;
		}
		return maxNum;
	}
};