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有一分?jǐn)?shù)序列：2/1，3/2，5/3，8/5，13/8，21/13...求出這個(gè)數(shù)列的前20項(xiàng)之和。
- 方法一
a,b = 1,1
s = 0
for i in range(20):
a,b = b, a+b
s += b/a
print('前二十項(xiàng)的和為{}'.format(s))
#前二十項(xiàng)的和為32.66026079864164
- 方法二
a,b = 1,1
li = []
for i in range(20):
a,b = b, a+b
li.append(b/a)
print(li)
print('前二十項(xiàng)的和為{}'.format(sum(li)))
**************************************************************
[2.0, 1.5, 1.6666666666666667, 1.6, 1.625, 1.6153846153846154, 1.619047619047619, 1.6176470588235294, 1.6181818181818182, 1.6179775280898876, 1.6180555555555556, 1.6180257510729614, 1.6180371352785146, 1.618032786885246, 1.618034447821682, 1.6180338134001253, 1.618034055727554, 1.6180339631667064, 1.6180339985218033, 1.618033985017358]
前二十項(xiàng)的和為32.66026079864164
- 方法三
from functools import reduce
a,b = 1,1
li = []
for i in range(20):
a,b = b, a+b
li.append(b/a)
s = reduce(lambda x,y:x+y, li)
print('前二十項(xiàng)的和為{}'.format(s))
#前二十項(xiàng)的和為32.66026079864164
這邊出現(xiàn)了一個(gè)高端點(diǎn)的函數(shù)叫:reduce（）
參考：https://www.runoob.com/python/python-func-reduce.html
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計(jì)算階乘和（1！+2！+3！+...+20?。?/h3>
- 方法一
n = eval(input('請輸入數(shù)字：'))
s = 0
for j in range(1,n+1):
a = 1#還原
for i in range(1,j+1):#計(jì)算每個(gè)n對應(yīng)的階乘
a = a*i
s += a
print(s)
#請輸入數(shù)字：20
#2561327494111820313
- 方法二
采用reduce()函數(shù)
from functools import reduce
s = 0
for n in range(1,21):
li = list(range(1,n+1))
a = reduce(lambda x,y:x*y,li)
s += a
print(s)
- 方法三
def factorial(n):
if n==1:
return 1
else:
return(n*factorial(n-1))
s = 0
li = []
for n in range(1,21):
a = 0
a = factorial(n)
li.append(a)
print(sum(li))
這個(gè)是遞歸法
這么寫也可以：
def factorial(n):
if n==1:
return 1
else:
return(n*factorial(n-1))
s = 0
for n in range(1,21):
a = 0
a = factorial(n)
s += a
print(s)
