# Task 1: Duplicate Removals
# Submitted by: Mohammad Sajid Anwar
# 
# You are given a string, $str, consisting of lowercase English letters.
# 
# Write a script to return the final string after all duplicate removals have been made. Repeat duplicate removals on the given string until we no longer can.
# 
# A duplicate removal consists of choosing two adjacent and equal letters and removing them.
# 
# Example 1
# Input: $str = 'abbaca'
# Output: 'ca'
# 
# Step 1: Remove 'bb' => 'aaca'
# Step 2: Remove 'aa' => 'ca'
# 
# Example 2
# Input: $str = 'azxxzy'
# Output: 'ay'
# 
# Step 1: Remove 'xx' => 'azzy'
# Step 2: Remove 'zz' => 'ay'
# 
# Example 3
# Input: $str = 'aaaaaaaa'
# Output: ''
# 
# Step 1: Remove 'aa' => 'aaaaaa'
# Step 2: Remove 'aa' => 'aaaa'
# Step 3: Remove 'aa' => 'aa'
# Step 4: Remove 'aa' => ''
# 
# Example 4
# Input: $str = 'aabccba'
# Output: 'a'
# 
# Step 1: Remove 'aa' => 'bccba'
# Step 2: Remove 'cc' => 'bba'
# Step 3: Remove 'bb' => 'a'
# 
# Example 5
# Input: $str = 'abcddcba'
# Output: ''
# 
# Step 1: Remove 'dd' => 'abccba'
# Step 2: Remove 'cc' => 'abba'
# Step 3: Remove 'bb' => 'aa'
# Step 4: Remove 'aa' => ''

import re

def get_noduplicate(str):
    str_orig = str

    while re.search(r'([a-z])\1', str):
        str = re.sub(r'([a-z])\1', r'', str)

    print("'%s' -> '%s'" % ( str_orig, str ) )

if __name__ == "__main__":
    str = 'abbaca'
    get_noduplicate(str)

    str = 'azxxzy'
    get_noduplicate(str)

    str = 'aaaaaaaa'
    get_noduplicate(str)

    str = 'aabccba'
    get_noduplicate(str)

    str = 'abcddcba'
    get_noduplicate(str)