Python第一周 学习笔记（2）

习题解析

0.打印10以内偶数：位运算

for i in range(10):
if not i & 0x01:
print(i)

1.给定一个不超过5位的正整数，判断其有几位（使用input函数）

方法一：正常逻辑处理

a = int(input("Please enter a numer: "))
if a < 0:
print('Error')
if a < 10:
print(1)
elif a < 100:
print(2)
elif a < 1000:
print(3)
elif a < 10000:
print(4)
elif a < 100000:
print(5)
else:
print('Error')

方法二：折半

a=int(input("Please enter a numer: "))
if a < 0:
print('Error')
elif a < 1000:
if 9 < a < 100:
print(2)
elif a < 10:
print(1)
else:
print(3)
elif a < 10000:
print(4)
elif a < 100000:
print(5)
else:
print('Error')

方法三：字符串处理

a = str(int(input("Please enter a number: ")))
print(len(a))

2.给定一个不超过5位的正整数，判断该数的位数，依次打印出个位、十位、百位、千位、万位的数字

方法一：

a = int(input("Please enter a number: "))
length = 0
if a < 0:
print('Error')
elif a < 1000:
if 9 < a < 100:
length = 2
elif a < 10:
length = 1
else:
length = 3
elif a < 10000:
length = 4
elif a < 100000:
length = 5
else:
print('Error')
print(length)
for i in range(length):
print(a % 10)
a = a // 10

方法二：

a = input("Please enter a number: ")
b = int(a)
print(len(a))
for i in range(len(a)):
print(b % 10)
b = b // 10

方法三：

a = int(input("Please enter a number: "))
length = 0
if a < 0:
print('Error')
elif a < 1000:
if 9 < a < 100:
length = 2
elif a < 10:
length = 1
else:
length = 3
elif a < 10000:
length = 4
elif a < 100000:
length = 5
else:
print('Error')
print(length)
for i in range(length):
print(a - (a // 10) * 10)
a = a // 10

方法四：

a=int(input("Please enter a number: "))
a *= 10
while (a // 10) != 0:
a //= 10
print(a % 10)

3.给定一个不超过5位的正整数，判断该数的位数，依次打印出万位、千位、百位、十位、个位的数字

方法一：

a=input('Please enter a number: ')
b=int(a)
for i in range(len(a),0,-1):
te = 10 ** (i - 1)
c = b // te
print(c)
b -= (c * te)
print(len(a))

方法二：

a = int(input("Please enter a number: "))
length = 0
if a < 0:
print('Error')
elif a < 1000:
if 9 < a < 100:
length = 2
elif a < 10:
length = 1
else:
length = 3
elif a < 10000:
length = 4
elif a < 100000:
length = 5
else:
print('Error')
print(length)
pre = 0
for i in range(length,0,-1):
cur = a // (10 ** (i - 1))
print(cur - pre * 10)
pre = cur

方法三：

a = int(input("Please enter a number: "))
length = 0
if a < 0:
print('Error')
elif a < 1000:
if 9 < a < 100:
length = 10
elif a < 10:
length = 1
else:
length = 100
elif a < 10000:
length = 1000
elif a < 100000:
length = 10000
else:
print('Error')

while length:
print(a // length)
a %= length
length //= 10

方法四：

c = int(input("Please enter a number: "))
w = 10000
length = 5
flag = False
while w:
t = c // w
if flag:
print(t)
else:
if t:
print(t)
flag = True
else:
length -= 1
c = c % w
w //= 10
print("The length of number is", length)

4.打印一个边长为n的正方形

方法一：

a = int(input("Please enter a number: "))
for i in range(a):
if i == 0 or i == a-1:
print('*' * a )
else:
print('*' + ' ' * (a - 2) + '*')

方法二：

a = int(input("Please enter a number: "))
print('*' * a)
for i in range(a - 2):
print('*' + ' ' * (a - 2) + '*')
else:
print('*' * a)

方法三：

a = int(input("Please enter a number: "))
top = mid = '*'
for i in range(a - 1):
top += '\t*'
mid += '\t'
else:
mid += '*'
print(top)

for i in range(a - 2):
print('\n')
print(mid)
else:
print('\n')
print(top)

5.求100内所有奇数的和（2500）

方法一：

sum = 0
for i in range(1,100,2):
sum += i
print(sum)

6.判断学生成绩，成绩等级A~E。其中，90分以上为'A'，80~89分为'B'，70~79分为'C'，60~69分为'D'，60分以下为'E'

方法一：

a = int(input('Please enter a score: '))
if a > 79:
if a >= 90:
print('A')
else:
print('B')
elif a >= 70:
print('C')
elif 60 <= a < 69:
print('D')
else:
print('E')

7.求1到5阶乘之和

方法一：

sum = 0
for i in range(1,6):
mul = 1
for j in range(1,i + 1):
mul *= j
sum += mul
print(sum)

方法二：效率高

sum = 0
mul = 1
for i in range(1,6):
mul *= i
sum += mul
print(sum)

8.给一个数，判断它是否是素数（质数）

a=int(input("Please enter a number: "))
for i in range(2,int(a ** 0.5) + 1):
if a % i != 0:
continue
elif a % i == 0:
print(("N: %d") % (i))
break
else:
print("Yes,prime")

9.打印九九乘法表

for i in range(1,10):
line = ''
for j in range(1,i + 1):
line = line + ('%d*%d=%2d ') % (j,i,i*j)
print(line)

10.打印菱形

方法一：

a = int(input(">>>"))
b = (a - 1) / 2
for i in range(a):
if i <= b:
print(' ' * ((a - (2 * i + 1)) // 2) +'*' * (i * 2 + 1) + ' ' * (( a - (2 * i + 1)) // 2 ))
else:
m=int(2 * b - i)
print(' '*((a - (2 * m + 1)) // 2) +'*' * (m * 2 + 1) +' ' * ((a - (2 * m + 1)) // 2))

方法二：

a = int(input(">>>"))
b=(a - 1) // 2
for i in range(-b,b + 1):
c = abs(i)
print(' ' * c + '*' * (a - 2 * c) + ' ' * c)

11.打印100以内的斐波那契数列

a = 1
b = 1
while True:
ne = a + b
if ne >= 100:
break
a = b
b = ne
print(ne)

12.求斐波那契数列第101项 573147844013817084101

a = 1
b = 1
cnt = 2
while True:
ne = a + b
a = b
b = ne
cnt += 1
if cnt == 101:
print(b)
break

13.求10万内的所有素数 9592

方法一：

import datetime
start=datetime.datetime.now()
cnt=1
for i in range(3,100000,2):#优化点1：排除偶数
for j in range(3,int(i ** 0.5) + 1,2):#优化点2：排除含有因子2的数并只循环到原数的开方加1
if i % j == 0:
break
else:
#print(i)
cnt += 1
end=(datetime.datetime.now() - start).total_seconds()
print(end)
print(cnt)

方法二：

a = int(input('>>>'))
import datetime
start=datetime.datetime.now()
cnt = 2
for i in range(4,a):
if i % 6 != 1 and i % 6 != 5:#质数必与6的倍数相邻
continue
else:
for j in range(5,int(i ** 0.5) + 1,2):
if i % j == 0:
break
else:
cnt += 1
end=(datetime.datetime.now()-start).total_seconds()
print(end)
print(cnt)

方法三：

x = 5
step = 2
count = 2
while x < 100000:
for i in range(3,int(x ** 0.5) + 1,2):
if not x % i:
break
else:
count += 1
x += step
step = 4 if step == 2 else 2
print(count)

方法四：

prime=[2]
for i in range(3,100000,2):
flag=False
up=int(i**0.5)+1
for j in prime:
if i%j==0:
flag=False
break
if j>=up:
flag=True
break
if flag:
prime.append(i)
print(len(prime))

方法五：

筛选法
待补充

14.输入若干整数，打印最大值：

temp = 0
while True:
a = input('>>>')
if not a:
temp = a
break
else:
b = int(a)
if b >= temp:
temp = b
print(temp)

15.输入n个数，求每次输入后的算数平均数

sum = 0
cnt = 0
while True:
a = input('>>>')
if not a:
break
else:
sum += float(a)
cnt += 1
print(sum / cnt)

16.反向乘法表：

方法一：

for i in range(1,10):
line = ''
for j in range(i,10):
line += '%d*%d=%2d ' % (i,j,j * i)
print(' ' * (7 * i - 6) + line)

方法二：

for i in range(1,10):
line = ''
for j in range(i,10):
line += '%d*%d=%2d ' % (i,j,j * i)
print('{:>63}'.format(line))

方法三：

for i in range(1,10):
line = ''
for j in range(i,10):
line += '{}*{}={:<{}} '.format(i,j,j * i,2 if j<4 else 3)
print('{:>70}'.format(line))

17.打印对顶三角形：

a = int(input(">>>"))
b = (a - 1) // 2
for i in range(-b,b + 1):
c = int((a - (2 * abs(i) + 1)) / 2)
print(' ' * c + '*' * (2 * abs(i) + 1) + '  ' * c)

18.打印闪电：

num = int(input(">>>"))
if num % 2 == 0:
num += 1
half = (num - 1) // 2
for i in range(- half,half + 1):
if i < 0:
print(' ' * (-i) + '*' * (half + i + 1))
elif i == 0:
print('*' * num)
else:
print(' ' * half + '*' * (half - i + 1))

19.猴子吃桃：

x = 1
for i in range(9):
x = (x + 1) * 2
print(x)