Unique Paths

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?

Java

public class Solution {
    public int uniquePaths(int m, int n) {
        int[][] rst = new int[m][n];
        for(int i = 0; i < m; i++) {
            rst[i][0] = 1;
        }
        for(int i = 0; i < n; i++) {
            rst[0][i] = 1;
        }

        for(int i = 1; i < m; i++) {
            for(int j = 1; j < n; j++) {
                rst[i][j] = rst[i - 1][j] + rst[i][j - 1];
            }
        }

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