A robot is located at the top-left corner of amxngrid (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?

常規(guī)做法dp， 發(fā)現(xiàn)一個(gè)大神用組合的方式， Cnk?,? 從start 到end 有m+n-2 步要走， 向下走m-1步。
m+n-2 中向下走m-1 的組合方式 有C(m+n-2) (m-1) 種