杨辉三角

来源：廖雪峰-python-高级特性-生成器

杨辉三角规律：下一行的值为：上一行分别在前端和末尾添加0，形成两个新列表，两个新列表的每个元素相加得到的新列表。

实践：

在线 python 运行：菜鸟驿站

循环实现

#!/usr/bin/python
 
def triangles(max=10):
	arr = [1]
	n = 0
	while n < max:
		print(arr)
		arr1 = [0] + arr[:]
		arr2 = arr[:] + [0]
		arr = [arr1[i] + arr2[i] for i in range(len(arr1))]
		n += 1
		
triangles()

生成器实现

# -*- coding: utf-8 -*-

def triangles():
    arr = [1]
    while True:
        yield arr
        arr1 = [0] + arr[:]
        arr2 = arr[:] + [0]
        arr = [arr1[i]+arr2[i] for i in range(len(arr1))]
        
# 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():
    results.append(t)
    n = n + 1
    if n == 10:
        break

for t in results:
    print(t)

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!')

在线js运行: jsbin.com

js 实现-循环

function triangles(max = 10) {
  const arr = [1]
  let n = 0
  while (n < max) {
    console.log(arr)
    const arr1 = [0, ...arr]
    const arr2 = [...arr, 0]
    arr1.forEach((item, i) => arr[i] = arr1[i] + arr2[i])
    n++
  }
}

triangles()

js 迭代器实现

function *triangles() {
  const arr = [1]
  let n = 0
  while (true) {
    yield arr
    const arr1 = [0, ...arr]
    const arr2 = [...arr, 0]
    arr1.forEach((item, i) => arr[i] = arr1[i] + arr2[i])
  }
}

const res = triangles()

Array(10).fill(1).forEach((item, i) => {
  console.log(res.next().value)
})