leetcode——238——Product of Array Except Self

Given an array of n integers where n > 1,

nums

, return an array

output

such that

output[i]

is equal to the product of all the elements of

nums

except

nums[i]

.
Solve it without division and in O(n).

For example, given

[1,2,3,4]

, return

[24,12,8,6]

.

设得到数组A[],需得到B[i] = A[0]*A[1]...*A[i-1]*A[i+1]*....A[n-1],令C[i] = A[0]*A[1]...*A[i-1],D[i] = A[i+1]*....A[n-1],可得C[i] = C[i-1]*A[i-1],D[i] = D[i+1]*A[i+1],

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

}
};