Hello and welcome to our exciting exploration of PHP string manipulation! Today's lesson is particularly interesting: you will learn how to access characters from a string following a distinctive pattern using PHP. Our presentation is both comprehensive and concise, allowing you to master the concept quickly. Let's get started!

Imagine this: You receive a string, from which you need to extract characters, but the sequence in which you select them diverges from the norm. You start with the first character, then select the last character, move to the second character, then choose the second-to-last character, and continue this pattern until there are no characters left. Quite a mind-bender, isn't it?

Here's what we mean:

You are required to craft a PHP function, solution($inputString), within a PHP script. This function takes $inputString as a parameter, a string of lowercase English alphabet letters ('a' to 'z'), with a length ranging between 1 to 100 characters. The function then returns a new string, fashioned from the input string, but with characters selected in the pattern we described above.

For example, if the $inputString is "abcdefg", the function should return "agbfced".

Before we delve into the problem-solving aspect, let's arrange our result store. We initialize a variable, $result, as an empty string to stockpile the output.

php
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1<?php
2
3function solution($inputString) {
4    $result = '';

Upon initialization, we need to traverse the $inputString. PHP furnishes a for loop to iterate over the elements in a string efficiently.

Now, the question arises: What is the requisite number of iterations for our loop? Given that we select two characters per iteration — one from the beginning and one from the end — we need the loop to run for half of the string's length if the length is even or half the length plus one if it's odd to include the middle character.

We can realize this by employing intdiv(strlen($inputString), 2) + strlen($inputString) % 2. This ensures the loop iterates for half the length if it is even and half the length plus one if it's odd.

Here's our function thus far:

php
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1<?php
2
3function solution($inputString) {
4    $result = '';
5    $length = strlen($inputString);
6    for ($i = 0; $i < intdiv($length, 2) + $length % 2; $i++) {
7        // Implementation in the next step

Now that we are nested inside our loop, we can select characters and add them to our $result.

First, we fetch the character from the beginning of the input string using $inputString[$i], and append this to our $result.

Next, we secure the character from the end of the input string. We compute its index using $length - 1 - $i. However, we must make certain that we only add this character if it's different from the one we've selected from the start. This situation can arise when the string's length is odd, and we encounter the middle character. Therefore, we only append it if $length - 1 - $i is not equal to $i.

Incorporating these steps, our function evolves to:

php
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1<?php
2
3function solution($inputString) {
4    $result = '';
5    $length = strlen($inputString);
6    for ($i = 0; $i < intdiv($length, 2) + $length % 2; $i++) {
7        $result .= $inputString[$i];
8        if ($length - 1 - $i != $i) {
9            $result .= $inputString[$length - 1 - $i];
10        }
11    }
12    return $result;
13}
14
15// Example usage
16$inputString = "abcdefg";
17$outputString = solution($inputString);
18echo $outputString;  // Outputs: agbfced
19

And there you have it, our function is now complete!

Congratulations! In this lesson, you have mastered a unique aspect of string manipulation in PHP. Although it may have appeared challenging at first, your perseverance has indeed paid off! Now, the process of selecting characters from a string in such an unusual pattern should feel intuitive.

Now it's time for some practice. As the adage goes, "practice makes perfect," and it holds true here as well. The most effective way to cement your understanding of a concept is to apply it. Challenge yourself with other problems that require similar techniques. Not only will this exercise embed these concepts in your mind, but it will also enhance your confidence in problem-solving. Enjoy coding, and remember, persistence is key!