PHP Program to Find Most Frequent Character

Use count_chars($string, 1) to count characters, then find the max count and its character with array_search(max($counts), $counts) to get the most frequent character in PHP.

Examples

Inputhello

Outputl

Inputmississippi

Outputi

Inputaabbcc

Outputa

How to Think About It

To find the most frequent character, count how many times each character appears in the string. Then, find which character has the highest count. Return that character as the most frequent one.

Algorithm

1

Get the input string.

2

Count the frequency of each character in the string.

3

Find the character with the highest frequency count.

4

Return that character as the most frequent character.

Code

php

<?php
$string = "mississippi";
$counts = count_chars($string, 1);
$maxCount = max($counts);
$mostFrequentChar = chr(array_search($maxCount, $counts));
echo $mostFrequentChar;
?>

Output

i

Dry Run

Let's trace the string 'mississippi' through the code to find the most frequent character.

1

Input string

$string = 'mississippi'

2

Count characters

$counts = count_chars('mississippi', 1) gives array with counts: m=1, i=4, s=4, p=2

3

Find max count

$maxCount = max($counts) = 4

4

Find character with max count

$mostFrequentChar = chr(array_search(4, $counts)) = 'i'

5

Output result

echo 'i'

Character	Count
m	1
i	4
s	4
p	2

Why This Works

Step 1: Counting characters

The count_chars function counts how many times each character appears in the string and returns an array with character codes as keys and counts as values.

Step 2: Finding the maximum count

Using max() on the counts array finds the highest number of occurrences among all characters.

Step 3: Getting the character

The array_search() finds the character code that matches the max count, and chr() converts that code back to the character.

Alternative Approaches

Using a loop and associative array

php

<?php
$string = "hello";
$freq = [];
for ($i = 0; $i < strlen($string); $i++) {
    $char = $string[$i];
    if (isset($freq[$char])) {
        $freq[$char]++;
    } else {
        $freq[$char] = 1;
    }
}
$maxChar = '';
$maxCount = 0;
foreach ($freq as $char => $count) {
    if ($count > $maxCount) {
        $maxCount = $count;
        $maxChar = $char;
    }
}
echo $maxChar;
?>

This method manually counts characters and is easy to understand but less concise than built-in functions.

Using array_reduce with str_split

php

<?php
$string = "banana";
$chars = str_split($string);
$freq = array_reduce($chars, function($carry, $char) {
    $carry[$char] = ($carry[$char] ?? 0) + 1;
    return $carry;
}, []);
$maxChar = array_keys($freq, max($freq))[0];
echo $maxChar;
?>

This uses functional programming style but is more complex for beginners.

Complexity: O(n) time, O(1) space

Time Complexity

The program loops through the string once to count characters, so it runs in linear time relative to string length.

Space Complexity

It uses a fixed-size array for character counts (256 ASCII chars), so space is constant.

Which Approach is Fastest?

Using count_chars is fastest and simplest; manual loops are more flexible but slower.

Approach	Time	Space	Best For
count_chars function	O(n)	O(1)	Quick and efficient for ASCII strings
Manual loop with associative array	O(n)	O(n)	Flexible for any character set
array_reduce with str_split	O(n)	O(n)	Functional style, less readable for beginners