https://leetcode.com/problems/product-of-array-except-self/

题意：求数组中每个元素，不包括自己的乘积

思考：对于数组中的每一个数，我可以画成左边数的乘积*右边数的乘积

class Solution {
public:vector<int> productExceptSelf(vector<int>& nums) {int N = nums.size();vector<int> ret(N, 1);vector<int> left(N, 1);vector<int> right(N, 1);for(int i = 0; i < N; i++) {if( i == 0) {left[i] = 1;} else {left[i] = left[i-1]* nums[i-1];}}for(int i = N-1; i >= 0; i--) {if (i == N - 1) {right[i] = 1;} else {right[i] = right[i+1]*nums[i+1];}}for(int i = 0; i < N; i++) {ret[i] = left[i] * right[i];}  return ret;}
};