PHP Exercises: Check if the first appearance of "a" in a given string is immediately followed by another "a"

PHP Basic Algorithm: Exercise-28 with Solution

Write a PHP program to check if the first appearance of "a" in a given string is immediately followed by another "a".

Sample Solution:

PHP Code :

<?php
// Define a function that checks for the presence of at least two consecutive 'a's in a string
function test($s)
{
    // Initialize a counter for 'a' occurrences
    $counter = 0;

    // Iterate through the string
    for ($i = 0; $i < strlen($s) - 1; $i++) {
        // Check for 'a' and increment the counter
        if (substr($s, $i, 1) == 'a') {
            $counter++;
        }

        // Check for 'aa' and if counter is less than 2, return true
        if ((substr($s, $i, 2) == 'aa') && $counter < 2) {
            return true;
        }
    }

    // If no condition met, return false
    return false;
}

// Test the function with different input strings
var_dump(test("caabb"));
var_dump(test("babaaba"));
var_dump(test("aaaaa"));
?>

Explanation:

• Function Definition:
• The test function takes one parameter, $s, which is a string. It checks if there are two consecutive 'a' characters ("aa") with only one or no 'a' characters before it.
• Initialize Counter:
• A variable $counter is initialized to 0 to count occurrences of individual 'a' characters.
• Loop Through String:
• A for loop iterates through each character of the string up to the second-to-last character (strlen($s) - 1).
• Count Single 'a' Characters:
• Within the loop, if the character at the current position is 'a', $counter is incremented by 1.
• Check for Consecutive "aa":
• If two consecutive characters ("aa") are found, the function checks if $counter is less than 2.
• If true, it returns true, meaning at least one "aa" was found with fewer than 2 previous 'a' characters.
• Return False if No "aa" Matches Found:
• If the loop completes without finding "aa" that meets the condition, the function returns false.

Output:

bool(true)
bool(false)
bool(true)

Visual Presentation:

Flowchart:

PHP Code Editor:

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