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