LeetCode·152. Maximum Product Subarray

题目：

152. Maximum Product Subarray
Given an integer array nums, find the contiguous subarray within an array (containing at least one number) which has the largest product.

Example 1:

Input: [2,3,-2,4]
Output: 6
Explanation: [2,3] has the largest product 6.
Example 2:

Input: [-2,0,-1]
Output: 0
Explanation: The result cannot be 2, because [-2,-1] is not a subarray.

思路：

1. 动态规划；
2. 保留上次计算的结果，包括最大值和最小值；
3. 写出动态转移方程（见代码）；

代码：

我的解法：

class Solution {
public:
    int maxProduct(vector<int>& nums) {
        if(nums.size() < 1)return 0;
        int pre_maxs = nums[0];
        int pre_mins = nums[0];
        int g_max = nums[0];

        for(int i = 1; i < nums.size(); ++i){
            int max_c = pre_maxs;
            pre_maxs = max(pre_mins*nums[i], max(nums[i], nums[i]*pre_maxs));
            pre_mins = min(max_c*nums[i], min(nums[i], nums[i]*pre_mins));
            if(g_max < pre_maxs)
                g_max = pre_maxs;
        }

        return g_max;
    }
};

最优解法：

class Solution {
public:
    int maxProduct(vector<int>& a) {

        int l = a.size();

        int maxval = a[0];
        int minval = a[0];
        int ans = a[0];

        for(int i=1;iif(a[i]<0)
                swap(maxval,minval);

            maxval = max(a[i],maxval*a[i]);
            minval = min(a[i],minval*a[i]);

            ans = max(ans,maxval);
        }
        return ans;
    }
};

结果：