62.Unique Paths
===

###### tags: `Medium` `Math` `DP` `Combinatorics`

[62. Unique Paths](https://leetcode.com/problems/unique-paths/)

### 題目描述

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 tries to move to the **bottom-right corner** (i.e., `grid[m - 1][n - 1]`). The robot can only move either down or right at any point in time.

Given the two integers `m` and `n`, return *the number of possible unique paths that the robot can take to reach the bottom-right corner.*

The test cases are generated so that the answer will be less than or equal to 2 * 10^9^.

### 範例

**Example 1:**


Input: m = 3, n = 7
Output: 28

**Example 2:**

Input: m = 3, n = 2
Output: 3
Explanation: From the top-left corner, there are a total of 3 ways to reach the bottom-right corner:
1. Right -> Down -> Down
2. Down -> Down -> Right
3. Down -> Right -> Down

**Constraints**:

* 1 <= `m`, `n` <= 100

### 解答

### Reference

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