Pairing Opposite Characters in String | CodeSignal Learn

Pairing Opposite Characters in String | CodeSignal Learn

Introduction

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!

Task Statement

Solution Building: Step 1 - Initialization

Before we delve into the problem-solving aspect, let's arrange our result store. We initialize a variable, $result, as an empty string to stockpile the output. PHP <?php function solution($inputString) {$result = '';

Step 2 - Looping over the string

Sign up

Join the 1M+ learners on CodeSignal

Be a part of our community of 1M+ users who develop and demonstrate their skills on CodeSignal

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

<?php

function solution($inputString) {
    $result = '';
    $length = strlen($inputString);
    for ($i = 0; $i < intdiv($length, 2) + $length % 2; $i++) {
        // Implementation in the next step

Step 3: Adding Characters to the Result

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 $i . Incorporating these steps, our function evolves to: PHP <?php function solution($inputString) {$result = ''; $length = strlen($inputString); for ($i = 0; $i < intdiv($length, 2) + $length % 2; $i++) {$result .= $inputString[$i]; if ($length - 1 - $i != $i) {$result .= $inputString[$length - 1 - $i];}} return $result;} // Example usage $inputString = "abcdefg"; $outputString = solution($inputString); echo $outputString; // Outputs: agbfced And there you have it, our function is now complete!