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Problem 15


Problem 15


Lattice paths

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?


网格路径

从一个2×2方阵的左上角出发,只允许向右或向下移动,则恰好有6条通往右下角的路径。

对于20×20方阵来说,这样的路径有多少条?