[LeetCode] 152. Maximum Product SubarrayeetCode] 152. Maximum Product Subarray（积最大的子数组）

• Difficulty: Medium

• Related Topics: Array, Dynamic Programming

• Link: https://leetcode.com/problems/maximum-product-subarray/

Description

Given an integer array nums, find the contiguous subarray within an array (containing at least one number) which has the largest product.
给定一个整数数组 nums，找到积最大的子数组（至少包含一个整数）。

Examples

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.

Solution

这题看上去和最大子数组类似，只是把和最大变成了积最大。但是做法就发生了变化，由于无论怎么乘，结果的绝对值都是递增的（当然，0 的情况需要单独讨论）。所以，只要算一遍前缀和，一遍后缀和，就能得到结果。代码如下：

class Solution {
    fun maxProduct(nums: IntArray): Int {
        var result = nums[0]
        var left = 0
        var right = 0

        for (i in nums.indices) {
            left = (if (left == 0) 1 else left) * nums[i]
            right = (if (right == 0) 1 else right) * nums[nums.lastIndex - i]

            result = maxOf(result, left, right)
        }

        return result
    }
}