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Question 90

Question

Please write a program which count and print the numbers of each character in a string input by console.

Example: If the following string is given as input to the program:

abcdefgabc

Then, the output of the program should be:

a,2
c,2
b,2
e,1
d,1
g,1
f,1

Hints

Use dict to store key/value pairs. Use dict.get() method to lookup a key with default value.

Main author's Solution: Python 2

dic = {}
s=raw_input()
for s in s:
    dic[s] = dic.get(s,0)+1
print '\n'.join(['%s,%s' % (k, v) for k, v in dic.items()])

My Solution: Python 3

import string

s = input()
for letter in string.ascii_lowercase:
    cnt = s.count(letter)
    if cnt > 0:
        print("{},{}".format(letter,cnt))

OR

s = input()
for letter in range(ord('a'),ord('z')+1):    # ord() gets the ascii value of a char
    letter = chr(letter)                     # chr() gets the char of an ascii value
    cnt = s.count(letter)
    if cnt > 0:
        print("{},{}".format(letter,cnt))

Question 91

Question

Please write a program which accepts a string from console and print it in reverse order.

Example: If the following string is given as input to the program:*

rise to vote sir

Then, the output of the program should be:

ris etov ot esir

Hints

Use list[::-1] to iterate a list in a reverse order.

Main author's Solution: Python 2

s=raw_input()
s = s[::-1]
print s

My Solution: Python 3

s = input()
s = ''.join(reversed(s))
print(s)

Question 92

Question

Please write a program which accepts a string from console and print the characters that have even indexes.

Example: If the following string is given as input to the program:

H1e2l3l4o5w6o7r8l9d

Then, the output of the program should be:

Helloworld

Hints

Use list[::2] to iterate a list by step 2.

Main author's Solution: Python 2

s=raw_input()
s = s[::2]
print s

My Solution: Python 3

s = "H1e2l3l4o5w6o7r8l9d"
s = [ s[i] for i in range(len(s)) if i%2 ==0 ]
print(''.join(s))

OR

s = "H1e2l3l4o5w6o7r8l9d"
ns =''
for i in range(len(s)):
    if i % 2 == 0:
        ns+=s[i]
print(ns)

Question 93

Question

Please write a program which prints all permutations of [1,2,3]

Hints

Use itertools.permutations() to get permutations of list.

Solution:

import itertools
print list(itertools.permutations([1,2,3]))

Question 94

Question

Write a program to solve a classic ancient Chinese puzzle: We count 35 heads and 94 legs among the chickens and rabbits in a farm. How many rabbits and how many chickens do we have?

Hints

Use for loop to iterate all possible solutions.

Solution:

def solve(numheads,numlegs):
    ns='No solutions!'
    for i in range(numheads+1):
        j=numheads-i
        if 2*i+4*j==numlegs:
            return i,j
    return ns,ns

numheads=35
numlegs=94
solutions=solve(numheads,numlegs)
print solutions

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