```
//C(m-1,m+n-2)=(m+n-2)/(m-1) * (m+n-3)/(m-2) * n/1
class Solution {
public:
int uniquePaths(int m, int n) {
if(!(m&&n)) return 0;
double result=1;
for(int i=1;i<=m-1;i++)
{
result=result*(m+n-i-1)/(m-i);
}
return (int)result;
}
};
```

Code above got WA...