Hackerrank - Super Reduced String Solution

Steve has a string of lowercase characters in range ascii[‘a’..’z’]. He wants to reduce the string to its shortest length by doing a series of operations. In each operation he selects a pair of adjacent lowercase letters that match, and he deletes them. For instance, the string aab could be shortened to b in one operation.

Steve’s task is to delete as many characters as possible using this method and print the resulting string. If the final string is empty, print Empty String

Function Description

Complete the superReducedString function in the editor below. It should return the super reduced string or Empty String if the final string is empty.

superReducedString has the following parameter(s):

• s: a string to reduce

Input Format

A single string, .

Constraints

Output Format

If the final string is empty, print Empty String; otherwise, print the final non-reducible string.

Sample Input 0

aaabccddd

Sample Output 0

abd

Explanation 0

Steve performs the following sequence of operations to get the final string:

aaabccddd → abccddd → abddd → abd

Sample Input 1

aa

Sample Output 1

Empty String

Explanation 1

aa → Empty String

Sample Input 2

baab

Sample Output 2

Empty String

Explanation 2

baab → bb → Empty String

Solution in Python

import re

def superReducedString(s):
    while re.search(r"(\w)\1", s):
        s = re.sub(r"(\w)\1", "", s)
    return s or "Empty String"
print(superReducedString(input()))

Answer explanation

The question says "In each operation, he selects a pair of adjacent lowercase letters that match, and he deletes them."
Which means we have to remove any 2 repeating characters.

I have used a while loop because we have to replace all 2 repeating characters, and not only one.

CASE A

Example let our string s = "aabbabb"

In our first loop re.search will match "aa".

We use re.search only to check if there is any repeating characters. Then we will use re.sub to remove any 2 repeating character

s = "aabbabb"

Loop 1.
Matches -> "aa" ,"bb", "bb"
New String -> "a"

No more two repeating characters.
Output -> "a"

CASE B

Example let our string s = "abbabb"

In our first loop re.search will match "bb".

Then we will use re.sub to remove any 2 repeating character

s = "abbabb"

Loop 1.
Matches -> "bb" , "bb"
New String -> "aa"

Loop 2.
Match -> "aa"
New String -> ""

No more two repeating characters.
Output -> "Empty String"