# This Python file uses the following encoding: utf-8
# 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?
# pictures see at https://projecteuler.net/problem=15
import time
start = time.time()
def factorial(n):
sum = 1
for i in range(2, n+1):
sum *= i
return sum
print "%s ways ways found in %s seconds" % (factorial(40)/(factorial(20)*factorial(20)), time.time() - start)
Euler Project question 15 in python way
原文：http://www.cnblogs.com/cyberpaz/p/4042180.html