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 ofnums
except nums[i]
.
Solve it without division and in O(n).
For example, given [1,2,3,4]
, return [24,12,8,6]
.
這道題主要是不能用除法(用除法要判斷除數是否爲零,以及幾個零),所以維持兩個數組,一個表示左邊的積一個表示右邊的積。
class Solution {
public:
vector<int> productExceptSelf(vector<int>& nums) {
int sz = nums.size();
vector<int> left(sz, 1);
vector<int> right(sz, 1);
for(int i=1; i < sz; i++){
left[i] = left[i-1] * nums[i-1];
right[sz-1-i] = right[sz-i] * nums[sz-i];
}
vector<int> res(sz, 1);
for(int i = 0; i < sz; i++){
res[i] = left[i] * right[i];
}
return res;
}
};