```
public class Solution {
public int uniquePaths(int m, int n) {
if (m == 0 || n == 0) return 0;
int[][] f = new int[m][n];
for (int i = 0; i < m; i ++)
f[i][0] = 1;
for (int i = 0; i < n; i ++)
f[0][i] = 1;
for (int i = 1; i < m; i ++)
for (int j = 1; j < n; j ++)
f[i][j] = f[i - 1][j] + f[i][j - 1];
return f[m - 1][n - 1];
}
}
```