leetcode解题方案--152--Maximum Product Subarray

题目

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.

分析

动态规划
因为负负得正，所以要记录负数的最大值。 两次动态规划。

class Solution {   public static int maxProduct(int[] nums) {        int[] dpp = new int[nums.length];        int[] dpn = new int[nums.length];        dpp[0] = nums[0] > 0 ? nums[0] : 0;        dpn[0] = nums[0] > 0 ? 0 : nums[0];        int retn = dpn[0];        int retp = dpp[0];        for (int i = 1; i < nums.length; i++) {            if (nums[i] > 0) {                dpp[i] = (dpp[i - 1] == 0 ? 1 : dpp[i - 1]) * nums[i];                dpn[i] = (dpn[i - 1] == 0 ? 0 : dpn[i-1])*nums[i];            } else if (nums[i] < 0) {                dpn[i] = (dpp[i - 1] == 0 ? 1 : dpp[i - 1]) * nums[i];                dpp[i] = (dpn[i - 1] == 0 ? 0 : dpn[i-1])*nums[i];            } else {                dpp[i] = 0;                dpn[i] = 0;            }            retp= Math.max(dpp[i], retp);            retn = Math.max(dpn[i],retn);        }        if (retp==0) {            return retn;        }        return retp;    }}

看到leetcode上解答还有左右各遍历一次的