import random

# 第一题
list=[]
for i in range(20):
    t=random.randint(1,100)#1-99
    list.append(t)

print(list)
list_Ou=[]
for i in range(20):
    if(i%2==0):
        list_Ou.append(list[i])
print(list_Ou)
list_Ou=sorted(list_Ou,reverse=True)
print(list_Ou)

count=0
for i in range(20):
    if(i%2==0):
        list[i]=list_Ou[count]
        count+=1

print(list)

运行效果：