题目：
A robot is located at the top-left corner of a m x ngrid (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.
链接： http://leetcode.com/problems/unique-paths/
题解：
测试：
原文：http://www.cnblogs.com/yrbbest/p/4436405.html