Leetcode 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?

Above is a 3 x 7 grid. How many possible unique paths are there?

Note: m and n will be at most 100.

Difficulty: Medium

Solution: DP

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