Unique Path

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

How many possible unique paths are there?

Code

public class Solution {
    public int uniquePaths(int m, int n) {
        //dp[i][j]: unique path from 0,0 to i,j
        if (m==0 || n==0) return 0;
        int[][] dp = new int[m][n];

        for (int i=0; i<m; i++){
            for (int j=0; j<n; j++){
                if (i==0 || j==0) dp[i][j]=1;
                else {
                    dp[i][j] = dp[i][j-1] + dp[i-1][j];
                }
            }
        }

        return dp[m-1][n-1];
    }
}