```
public int uniquePaths(int m, int n) {
int[][] dp = new int[m][n];
for (int i = 0; i < m; i++){
for (int j = 0; j < n; j++){
int top = i == 0 ? 0 : dp[i - 1][j];
int left = j == 0 ? 0 : dp[i][j - 1];
if (top + left == 0) dp[i][j] = 1;
else dp[i][j] = top + left;
}
}
return dp[m - 1][n - 1];
}
```