杨辉三角

练习
杨辉三角定义如下：

         1
        / \
       1   1
      / \ / \
     1   2   1
    / \ / \ / \
   1   3   3   1
  / \ / \ / \ / \
  1   4   6   4   1
 / \ / \ / \ / \ / \
1   5   10  10  5   1

把每一行看做一个list，试写一个generator，不断输出下一行的list：

# 期待输出:
# [1]
# [1, 1]
# [1, 2, 1]
# [1, 3, 3, 1]
# [1, 4, 6, 4, 1]
# [1, 5, 10, 10, 5, 1]
# [1, 6, 15, 20, 15, 6, 1]
# [1, 7, 21, 35, 35, 21, 7, 1]
# [1, 8, 28, 56, 70, 56, 28, 8, 1]
# [1, 9, 36, 84, 126, 126, 84, 36, 9, 1]
n = 0
results = []
for t in triangles():
    print(t)
    results.append(t)
    n = n + 1
    if n == 10:
        break
if results == [
    [1],
    [1, 1],
    [1, 2, 1],
    [1, 3, 3, 1],
    [1, 4, 6, 4, 1],
    [1, 5, 10, 10, 5, 1],
    [1, 6, 15, 20, 15, 6, 1],
    [1, 7, 21, 35, 35, 21, 7, 1],
    [1, 8, 28, 56, 70, 56, 28, 8, 1],
    [1, 9, 36, 84, 126, 126, 84, 36, 9, 1]
]:
    print('测试通过!')
else:
    print('测试失败!')

来源：
https://www.liaoxuefeng.com/wiki/0014316089557264a6b348958f449949df42a6d3a2e542c000/0014317799226173f45ce40636141b6abc8424e12b5fb27000#0

方法一

#果然真的厉害！！！
# -*- coding: utf-8 -*-
def triangles():
    ls = [1]
    while True:
        yield ls
        ls = [1] + [ls[i]+ls[i+1] for i in range(len(ls)-1)] + [1]

方法二

# python代码关键要简洁易懂 
# 杨辉三角的思路如下： 
# 某一行的数字是list b， 
# 则下一行计算如下： 
# 0, b0, b1, b2 
# + b0, b1, b2, 0 
# 即首尾各加一个0然后加起来 
def triangles(): 
    b = [1]  
    while True: 
        yield b 
        c = [0] + b 
        d = b + [0] 
        b = list(map(operator.add, c, d))

来源：
https://www.zhihu.com/question/39256042/answer/328053927