238. Product of Array Except Self

Given an array of n integerswhere n > 1, nums, return an array output suchthat output[i] is
equal to the product of all theelements of nums except nums[i].

Solve it withoutdivision and in O(n).

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

解题思路：

不使用除法，返回一个数组，数组中第i个元素的值为nums[1]*..nums[i-1]*nums[i+1]…nums[n-1]。

利用前n个元素的乘积数组和后n个数组的乘积数组，得到结果。

暂时是能达到60ms

class Solution {
public:
vector<int> productExceptSelf(vector<int>& nums) {
int n=nums.size();
vector<int>a=vector<int>(n,0);
a[0]=1;
for(int i=1;i<n;i++){
a[i]=a[i-1]*nums[i-1];
}
for(int i=n-1;i>0;i--){
a[i-1]=a[i-1]*nums[i];
nums[i-1]=nums[i]*nums[i-1];
}
//for(int i=0;i<n;i++)cout<<a[i]<<" ";
return a;
}
};