[FIXED] Capital M is encountered, duplicate previous character (then remove the M), and capital N is encountered remove the next character from the string

Issue

• Whenever a capital 'M' is encountered, duplicate the previous character (then remove the 'M')
• Whenever a capital 'N' is encountered remove the next character from the string (then remove the 'N').
• All other characters in the string will be lowercase letters.
• For example: "abcNdgM" should return "abcgg". The final string will never be empty.

def StringChanges(str):
    str2 = []
    list = ""

    for i in str:
        if i == 'M':
            str2.pop(i)
            str -= 1
            i -= 1
        elif i == 'N':
            if i == list - 1:
                str2.pop()
        else:
             str2.append(i)
             list -= 2
             i -= 2
    return ''.join(str2)

str = "oMoMkkNrrN"

print(StringChanges(str))

Solution

Use re.sub like so:

import re
strings = ['abcNdgM', 'abcdg', 'MrtyNNgMM']

for s in strings:
    # Repeat the cycles of transforming M/N with previous or subsequent characters:
    while True:
        s_new = re.sub(r'N.', '', re.sub(r'(.)M', r'\1\1', s))
        if s == s_new:
            break
        s = s_new
    # Remove any remaining Ms and Ns:
    s = re.sub(r'[MN]+', '', s)
    print(s)
# abcgg
# abcdg
# rtyggg

r'STRING': raw string.
. : any 1 character.
\1 : capture group 1, that is, whatever was matched by the pattern inside the parentheses.

Answered By - Timur Shtatland