comb.py

#!/usr/bin/env python
# coding: utf8
def comb(n, r):
    "calc combination"
    if n == 0 or r == 0: return 1
    # return (n - r + 1) / r * comb(n, r - 1)
    # 先にrで割ると，小数点を切り捨ててしまう
    return comb(n, r - 1) * (n - r + 1) / r

#print comb(10, 2) # 45

def pascal(x):
    import sys
    print_no_space = sys.stdout.write
    for n in xrange(0, x+1):
        print_no_space(' ' * (x-n))
        for r in xrange(0, n+1):
            print comb(n, r),
        print

pascal(3)
#    1
#   1 1
#  1 2 1
# 1 3 3 1