Problem 15 - Starting in the top left corner in a 20 by 20 grid, how many routes are there to the bottom right corner?

링크

Starting in the top left corner of a 22 grid, there are 6 routes (without backtracking) to the bottom right corner.

How many routes are there through a 2020 grid?

40 C 20 (combination) 을 구하면 된다.

python

pascal = [[1, 0]] for i in range(1, 41): nextrow = [1] for j in range(1, i+1): nextrow.append(pascal[i-1][j] + pascal[i-1][j-1]) nextrow.append(0) pascal.append(nextrow) print pascal[40][20]