### https://theweeklychallenge.org/blog/perl-weekly-challenge-313/
"""

Task 2: Reverse Letters

Submitted by: [44]Mohammad Sajid Anwar
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   You are given a string.

   Write a script to reverse only the alphabetic characters in the string.

Example 1

Input: $str = "p-er?l"
Output: "l-re?p"

Example 2

Input: $str = "wee-k!L-y"
Output: "yLk-e!e-w"

Example 3

Input: $str = "_c-!h_all-en!g_e"
Output: "_e-!g_nel-la!h_c"
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   Last date to submit the solution 23:59 (UK Time) Sunday 23rd March
   2025.
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SO WHAT DO YOU THINK ?
"""
### solution by pokgopun@gmail.com

def rl(string: str) -> str:
    ltrPos = tuple(i for i in range(len(string)) if string[i].isalpha()) ### positions of letters
    chars = list(string) ### convert string to list so its letters can be reversed
    l = len(ltrPos)
    for i in range(l//2): ### do the reverse by swap a letter at start and end of the list unitl reaching the mid
        a, b = ltrPos[i], ltrPos[l-1-i]
        chars[a], chars[b] = chars[b], chars[a]
    return "".join(chars) ### compose the string back

import unittest

class TestRl(unittest.TestCase):
    def test(self):
        for inpt, otpt in {
                "p-er?l": "l-re?p",
                "wee-k!L-y": "yLk-e!e-w",
                "_c-!h_all-en!g_e": "_e-!g_nel-la!h_c",
                }.items():
            self.assertEqual(rl(inpt),otpt)

unittest.main()