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ProductofArrayExceptSelf.cpp
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ProductofArrayExceptSelf.cpp
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#include <vector>
using namespace std;
class Solution {
public:
/* Sol 0
* Without division and use O(n) time and O(1) space
*/
vector<int> productExceptSelf(vector<int>& nums) {
vector<int> result(nums.size(),1);
int len = nums.size(),right=1;
for(int i = 1;i < len;++i) result[i] = result[i-1] * nums[i-1];
for(int i = len-1;i >= 0;--i){
result[i]*=right;
right*=nums[i];
}
return result;
}
/* Sol 1
* If division is permitted, take good case of zero.
* When compute the product of all numbers, count the number of zeros.
* If there are more than one zero, the result is a zero-array.
* If there is exactly one zero, then only one position can be non-zero
*/
vector<int> productExceptSelf1(vector<int>& nums){
int len = nums.size(),product=1,counter=0;
vector<int> result(len,0);
for(auto n:nums){
if(n==0) {if(++counter>1) break;}
else product*=n;
}
if(counter>1) return result;
for(int i = 0;i < len;++i){
if(counter==0) result[i] = product / nums[i];
else if(nums[i]==0) result[i] = product;
}
return result;
}
};