题目是这样的:
Starting in the top left corner of a 2×2 grid, and only being able to move to the right and down, there are exactly 6 routes to the bottom right corner.
How many such routes are there through a 20×20 grid?
这个题来自 Project Euler 的第 15 题.翻译为中文的话,题意大致是:
从一个 2x2 的网络的左上角出发,只能向右或向下移动,到右下角一共有 6 种不同的走法.那么,对一个 20x