原题地址：https://oj.leetcode.com/problems/unique-paths/
题意：
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.
解题思路：这道题和climbing stairs很像，可以用动态规划解决。状态转移方程为dp[i][j]=dp[i-1][j]+dp[i][j-1]。
代码：
class Solution:
# @return an integer
def uniquePaths(self, m, n):
if m == 1 and n == 1:
list = [[1]]
elif m == 1 and n > 1:
list = [[1 for i in range(n)]]
elif m > 1 and n == 1:
list = [[1] for i in range(m)]
else:
list = [[0 for i in range(n)] for i in range(m)]
for i in range(0, n):
list[0][i] = 1
for i in range(0, m):
list[i][0] = 1
for i in range(1, m):
for j in range(1, n):
list[i][j] = list[i-1][j] + list[i][j-1]
return list[m-1][n-1]