Unique Paths

class Solution {
public:
    int num[110][110];
    int dfs(int m,int n,int x,int y)
    {
        if(num[x][y]) return num[x][y];
        if(x==m-1 && y==n-1) return 1;
        if(x+1<m) num[x][y]+=dfs(m,n,x+1,y);
        if(y+1<n) num[x][y]+=dfs(m,n,x,y+1);
        return num[x][y];
    }
    int uniquePaths(int m, int n) {
        memset(num,0,sizeof(num));
        return dfs(m,n,0,0);
    }
};