238. Product of Array Except Sel

题目描述

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.)

Qiang的思路

class Solution:
    def productExceptSelf(self, nums: List[int]) -> List[int]:
        res = [1 for _ in range(len(nums))]
        for i in range(1, len(nums)):
            res[i] = res[i-1] * nums[i-1]
        tmp = 1
        for i in range(len(nums)-2, -1, -1):
            tmp = tmp * nums[i+1]
            res[i] = tmp * res[i]
        return res

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        vector<int> res(nums.size());
        res[0]=1;
        for(int i=1; i<nums.size(); i++)
            res[i]=res[i-1]*nums[i-1];
        int tmp=1;
        for(int i=nums.size()-2; i>=0; i--){
            tmp*=nums[i+1];
            res[i]*=tmp;
        }
        return res;
    }
};