There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner (i.e., grid[m-1][n-1]).
Return the number of possible unique paths that the robot can take to reach the bottom-right corner.
Example 1:
Input: m = 3, n = 7
Output: 28
Explanation: From the top-left corner, there are 28 unique paths to reach the bottom-right corner.
Example 2:
Input: m = 3, n = 2
Output: 3
Explanation: There are three paths: Right → Down → Down, Down → Down → Right, Down → Right → Down.
Example 3:
Input: m = 1, n = 1
Output: 1
Explanation: The robot is already at the destination.
1 <= m, n <= 100