# 【LeetCode with Python】 62. Unique Paths

## 题目

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.

## 代码

class Solution:
# @return an integer
def uniquePaths(self, m, n):
if 0 == m or 0 == n:
return 1
up = 1
for i in range(m + n - 2, n - 1, -1):
up *= i
down = 1
for j in range(1, m):
down *= j
return up / down