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238. Product of Array Except Self

难度: Medium

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%

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;
    }
}


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