grid_unique_paths.cpp

class Solution{
public:
	int uniquePaths(int m, int n){
		int N = n+m-2;
		int r = m-1;
		double res = 1;

		for(int i=1;i<=r;i++){
			res = res*(N-r+i)/i;
		}
		return (int)res;
	}
};