LeetCode 62 Unique Paths - Problem Statement

A robot starts at the top-left corner of an m × n grid and wants to reach the bottom-right corner. It can only move right or down.

How many unique paths exist?

With m = 3, n = 7:

• Grid is 3 rows × 7 columns.
• Robot needs 2 down moves and 6 right moves in some order.
• Answer: $28$.

With m = 3, n = 2:

• RRD, RDR, DRR... wait, that's wrong. Actually RD, DR (only 1 right, 2 downs? No.)
• $m=3$ means 3 rows (2 down moves), $n=2$ means 2 columns (1 right move).
• Paths: DR, RD, DR... = $3$ paths.

Constraints: $1 \le m, n \le 100$.