python学习(13)

2023-01-31 04:01:49 python 学习

random.unifORM(a,b)
随机生成a,b之间的一个浮点数

random.uniform(1,20)
1.0130916166719703

习题1:生成[“z1”,”y2”,”x3”,”w4”,”v5”]

#coding=utf-8
result = []
for i in range(1,6):
    result.append(chr(122-i+1)+str(i))
print(result) 

#coding=utf-8
result = []
for i in range(1,6):
result.append(chr(97+i-1)+str(i))
print(result)

习题2:拼接一个字符串的首字母、末尾字母、中间字母为一个字符串
要考虑奇数偶数长度,如果只有1个2个字母的字符串

方式1:直接拼字符串

s = "abcdefghig"

result_str = ""
result_str += s[0]

if len(s)%2 == 1:
    middle_letter = s[len(s)//2]
else:
    middle_letter = s[len(s)//2-1]
    middle_letter += s[len(s)//2]

print(middle_letter)
result_str += middle_letter

result_str += s[-1]

print("拼接后的字符串: ",result_str)

方式2:利用列表

def join_str(s):
    result = []
    result.append(s[0])

    if len(s)%2==1:
        result.append(s[len(s)//2])
    else:
        result.append(s[len(s)//2-1])
        result.append(s[len(s)//2])

    result.append(s[-1])
    return "".join(result)

s = "abcdefghig"
s2 = "abcdefghi"
print("拼接后的字符串: ",join_str(s))
print("拼接后的字符串: ",join_st

切片没有越界

s = "a"
s[5:] #没有越界
''
s[5]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: string index out of range

a = [1]
a[0:1] = [1,2,3,4]
a
[1, 2, 3, 4]
a =[1]
a[0:2] = [1,2,3,4]
a
[1, 2, 3, 4]

a = [1]
a[0]
1
a[0] = [1,2,3,4]
a
[[1, 2, 3, 4]]

a = [1]
a[0:7]
[1]
a[0:7] = [1,2,3,4]
a
[1, 2, 3, 4]

a
[1, 2, 3, 4]
a[0:2] = [7,8,9,10]
a
[7, 8, 9, 10, 3, 4]

a[0] = [55,66]
a
[[55, 66], 8, 9, 10, 3, 4]

a[0:5] = [1]
a
[1, 4]

习题3:S = “i am, a boy ”把boy替换为m
利用切片赋值特性

算法:先把字符串转换为列表
遍历列表,找到boy字符串
替换boy字符串为m

#coding=utf-8
s = "i am, a    boy!!"

list_s = list(s)
sub_length = len("boy")

for i in range(len(list_s)):
    if "".join(list_s[i:i+sub_length]) == "boy":
        list_s[i:i+sub_length] = "m"#可以用切片直接替换
print("".join(list_s)) 

习题4:非递归实现生成斐波那契数列

#coding=utf-8
def fib(n):
    result = []
    if n <=0 or not isinstance(n,int):
        return result
    for i in range(n):
        if i < 2:
            result.append(1)
        else:
            result.append(result[i-1] +  result[i-2])
    return result
print("斐波那契数列: ",fib(5))
print("斐波那契数列: ",fib(-2))

习题5:非递归实现求第n项斐波那契数列值
算法:遍历n,如果n等于0或1直接返回1
如果n >=2,记录前面两个项的和,并重新记录新的第1个,第2个数;


#coding=utf-8
def fib(n):

    a,b=1,1
    sum = 0
    if n <=0 or not isinstance(n,int):
        return -1
    for i in range(n):
        if i < 2:
            sum = 1
        else:
            sum = a + b
            a = b
            b = sum
    return sum

print(fib(5))

习题6:递归求两个数的最大公约数
方式1:

算法:

找出两个数的较小数(第一次)
如果两个数除以较小数余数都等于0的话,添加到一个列表中
不然的话继续调用函数自身,并且num-1传入到num参数中。

def max_common_divisor(a,b,num=0,result=[]):

    if num == 0:
        if a < b:
            num = a
        else:
            num = b

    if a%num == 0 and b%num == 0:
        print(result)
        result.append(num)
    else:

       max_common_divisor(a,b,num-1)

    return result#函数递归调用结束后才会执行此代码

print(max_common_divisor(24,120))    

      

方式2:更相减损法

def get(small,big):
    if small > big:
        small,big = big,small

    if small == big:
        return small

    return get(small,big-small)

print(get(30,24))

方式3:辗转相除法

def gain(small, big):
    if small > big:
        small, big = big, small
    if small == 0:
        return big
    return gain(small, big % small)

习题7:利用递归,处理嵌套列表,生成列表[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
定义全局变量:(尽量不使用全局变量)

l = [1,2,[3,4,[5,6,7,[8,9,[10,11]]]]]
result  = []
def func(p):
    global result
    for v in p:
        if not isinstance(v,list):
            result.append(v)
        else:
            func(v)
    return result
print(func(l))

引用传参:

def get_list(l,result=[]):
    for v in l:
        if not isinstance(v,list):
            result.append(v)
        else:
            get_list(v)
    return result

l = [1,2,[3,4,[5,6,7,[8,9,[10,11]]]]]
print(get_list(l))

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