HackerRank Python: itertools.permutations() Solution

Table of Contents

Question

This tool returns successive r length permutations of elements in an iterable.

If r is not specified or is None, then r defaults to the length of the iterable, and all possible full length permutations are generated.

Permutations are printed in a lexicographic sorted order. So, if the input iterable is sorted, the permutation tuples will be produced in a sorted order.

_{Sample Code}

>>> from itertools import permutations
>>> print permutations(['1','2','3'])
<itertools.permutations object at 0x02A45210>
>>> 
>>> print list(permutations(['1','2','3']))
[('1', '2', '3'), ('1', '3', '2'), ('2', '1', '3'), ('2', '3', '1'), ('3', '1', '2'), ('3', '2', '1')]
>>> 
>>> print list(permutations(['1','2','3'],2))
[('1', '2'), ('1', '3'), ('2', '1'), ('2', '3'), ('3', '1'), ('3', '2')]
>>>
>>> print list(permutations('abc',3))
[('a', 'b', 'c'), ('a', 'c', 'b'), ('b', 'a', 'c'), ('b', 'c', 'a'), ('c', 'a', 'b'), ('c', 'b', 'a')]

Task

You are given a string S.

Your task is to print all possible permutations of size k of the string in lexicographic sorted order.

Input Format

A single line containing the space separated string S and the integer value k.

Constraints

$0 < k <= len(S)$
The string contains only UPPERCASE characters.

Output Format

Print the permutations of the string S on separate lines.

Sample Input

HACK 2

Sample Output

AC
AH
AK
CA
CH
CK
HA
HC
HK
KA
KC
KH

Explanation

All possible size 2 permutations of the string “HACK” are printed in lexicographic sorted order.

Solution

				
					from itertools import permutations

# Input
S, k = input().split()  # Splitting the input string S and integer k
k = int(k)  # Converting k to an integer

# Generate permutations
perms = permutations(sorted(S), k)

# Print permutations
for perm in perms:
    print(''.join(perm))

Explanation

First, we import the permutations function from the itertools module. This function generates permutations of elements from an iterable.
The input is read using the input() function, which reads a line of text from the user. The line is split into two parts: S, which represents the string, and k, which represents the size of the permutations.
The value of k is converted to an integer using the int() function to ensure it is a numerical value.
The permutations function is called with the sorted characters of the string S and the value of k as arguments. This generates an iterator that produces all possible permutations of size k from the characters of S. Sorting the characters ensures that the permutations are produced in lexicographic sorted order.
Next, we iterate over each permutation in the perms iterator using a for loop. For each permutation, we join the characters together using the ''.join(perm) statement to create a string representation of the permutation.
The resulting string is printed, representing one possible permutation of size k of the original string S.
The loop continues until all permutations have been printed.