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

Last update on May 28 2025 09:29:04 (UTC/GMT +8 hours)

28. First "a" Followed Immediately by Another "a"

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:

For more Practice: Solve these Related Problems:

• Write a PHP script to check if the first occurrence of the letter "a" in a string is directly followed by another "a".
• Write a PHP function to find the first "a" in a string and verify if the next character is also "a" using substring indexing.
• Write a PHP program to parse a string and determine if an "a" is immediately repeated after its first appearance.
• Write a PHP script to use regex to match the pattern "aa" at the beginning portion of the string and output a boolean result.

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