【LeetCode】238. Product of Array Except Self解题报告

【LeetCode】238. Product of Array Except Self解题报告

tags: Array

题目地址：https://leetcode.com/problems/product-of-array-except-self/#/description
题目描述：

  Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

  Solve it without division and in O(n).

  For example, given [1,2,3,4], return [24,12,8,6].

Solutions:

正解：

public class Solution {    public int[] productExceptSelf(int[] nums) {         int n = nums.length;    int[] res = new int[n];    res[0] = 1;    for (int i = 1; i < n; i++) {        res[i] = res[i - 1] * nums[i - 1];    }    int right = 1;    for (int i = n - 1; i >= 0; i--) {        res[i] *= right;        right *= nums[i];    }    return res;    }}

  起初题意理解错误，以为是任意2,3，。。。n个数的乘积都要输出，其实是n-1个数的乘积输出，且不可以用到除法。列出代码依次每一步的输出

    res[0]=1;res[1]=1*1=1;res[2]=1*2=2;res[3]=2*3=6;    right=1;res[3]=6*1=6;right=1*4=4;            res[2]=2*4=8;right=4*3=12;            res[1]=1*12=12;right=12*2=24;            res[0]=1*24=24;right=24*1=24;

Date：2017年6月3日