Скачать или смотреть First Repeating Alphanumeric Finder – Detailed Version

In this problem, you are given a string, and your task is to find the first occurrence of an alphanumeric character that has consecutive repetitions. In other words, we need to detect the first instance where a letter or digit is immediately repeated one or more times in the string. If such a repetition exists, we output that character; otherwise, we print -1.

This solution leverages Python’s powerful regular expressions via the re module. We use a capturing group in our regex pattern to detect a repeating alphanumeric character. The pattern used is:

([A-Za-z0-9])\1+
Here’s what each part does:

([A-Za-z0-9]): This part captures any alphanumeric character (both uppercase and lowercase letters, and digits) as a group.

\1+: This is a backreference that matches one or more occurrences of the same character captured by the first group.

Using re.search(), we search the input string for this pattern. If a match is found, m.group(1) returns the first repeating alphanumeric character. Otherwise, we output -1.

This detailed explanation covers key concepts such as #Regex, #CapturingGroups, and #Backreferences, making it an excellent example for learning how to apply regular expressions for string validation and pattern matching.

Code (Detailed Version):

import re

def solve():
Read the input string and strip any extra whitespace
s = input().strip()
Use regex to find the first occurrence of an alphanumeric character with consecutive repetitions
match = re.search(r'([A-Za-z0-9])\1+', s)
If a match is found, print the matched character, else print -1
if match:
print(match.group(1))
else:
print(-1)

if _name_ == '__main__':
solve()