Only one array is given for dp storage.

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