每周LeetCode算法题（十三）152. Maximum Product Subarray

每周LeetCode算法题（十三）

题目: 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.

解法分析

本题求最大连续乘积，目测O(n)时间复杂度即可。这道题最重要是要想到，最正的数乘上负数成了最负的数，反之最负的数乘上负数成了最正的数。因此用max_p和min_p来分别保存最正的数和最负的数（当然，可能也没有负数出现，那么最负的数就是最小的正数），再用ans来时刻记录当前乘积的最大值。

C++代码

class Solution {public:    int maxProduct(vector<int>& nums) {        int len = nums.size();        int ans = nums[0];        int max_p = nums[0];        int min_p = nums[0];        for (int i = 1; i < len; i++) {            if (nums[i] < 0) {                int tmp = max_p;                max_p = min_p;                min_p = tmp;            }            max_p = max(nums[i], max_p * nums[i]);            min_p = min(nums[i], min_p * nums[i]);            ans = max(ans, max_p);        }        return ans;    }};