# 238. Product of Array Except Self

**<font color=red>难度: Medium</font>**

## 刷题内容

> 原题连接

* https://leetcode.com/problems/two-sum

> 内容描述

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

Example:

Input:  [1,2,3,4]
Output: [24,12,8,6]
Note: Please solve it without division and in O(n).

Follow up:
Could you solve it with constant space complexity? (The output array does not count as extra space for the purpose of space complexity analysis.)
```

## 解题方案

> 思路 1
******- 时间复杂度: O(N)******- 空间复杂度: O(N)******

前缀积和后缀积, 懒得实现了


# Follow up:
Could you solve it with constant space complexity? (The output array does not count as extra space for the purpose of space complexity analysis.)

> 思路 1
******- 时间复杂度: O(N)******- 空间复杂度: O(1)******

还是一样的思想，只不过不记录下来，而是采用边循环边更新的方式

beats 100.00%


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

        return res;
    }
}
```
