PHP Program to Convert a Given Number to Words

Given an integer N, the task is to convert the given number into words using PHP.

Examples:

Input: N = 438237764
Output: Four Hundred Thirty Eight Million Two Hundred Thirty Seven Thousand Seven Hundred Sixty Four

Input: N = 1000
Output: One Thousand

Below are the approaches to convert a given number to words:

Using a Pre-defined Array of Words

In this method we use pre-defined arrays containing words for units, tens, and special cases like numbers 11-19. It processes the given number by breaking it down into its individual digits and constructs the word representation by concatenating the corresponding words from the arrays.

Example: Below is the implementation of the above approach to convert a given number to words.

PHP

<?php

function numToWords($number) {
    $units = array('', 'one', 'two', 'three', 'four',
                   'five', 'six', 'seven', 'eight', 'nine');

    $tens = array('', 'ten', 'twenty', 'thirty', 'forty',
                  'fifty', 'sixty', 'seventy', 'eighty', 
                  'ninety');

    $special = array('eleven', 'twelve', 'thirteen',
                     'fourteen', 'fifteen', 'sixteen',
                     'seventeen', 'eighteen', 'nineteen');

    $words = '';
    if ($number < 10) {
        $words .= $units[$number];
    } elseif ($number < 20) {
        $words .= $special[$number - 11];
    } else {
        $words .= $tens[(int)($number / 10)] . ' '
                  . $units[$number % 10];
    }

    return $words;
}

// Example usage:
$number = 90;
echo "Number $number in words: " 
      . numToWords($number);

?>

Output

Number 90 in words: ninety 

Time Complexity: O(Log₁₀(N))

Auxiliary Space: O(1)

Using Recursive Function for Large Numbers

In this approach we use recursive function to handle larger numbers by breaking them down into smaller parts, such as hundreds, thousands, or millions, and recursively converting each part into words.

Example: Below is the implementation of the above approach to convert a given number to words

PHP

<?php

function numToWordsRec($number) {
    $words = array(
        0 => 'zero', 1 => 'one', 2 => 'two',
        3 => 'three', 4 => 'four', 5 => 'five',
        6 => 'six', 7 => 'seven', 8 => 'eight',
        9 => 'nine', 10 => 'ten', 11 => 'eleven',
        12 => 'twelve', 13 => 'thirteen', 
        14 => 'fourteen', 15 => 'fifteen',
        16 => 'sixteen', 17 => 'seventeen', 18 => 'eighteen',
        19 => 'nineteen', 20 => 'twenty', 30 => 'thirty',
        40 => 'forty', 50 => 'fifty', 60 => 'sixty',
        70 => 'seventy', 80 => 'eighty',
        90 => 'ninety'
    );

    if ($number < 20) {
        return $words[$number];
    }

    if ($number < 100) {
        return $words[10 * floor($number / 10)] .
               ' ' . $words[$number % 10];
    }

    if ($number < 1000) {
        return $words[floor($number / 100)] . ' hundred ' 
               . numToWordsRec($number % 100);
    }

    if ($number < 1000000) {
        return numToWordsRec(floor($number / 1000)) .
               ' thousand ' . numToWordsRec($number % 1000);
    }

    return numToWordsRec(floor($number / 1000000)) .
           ' million ' . numToWordsRec($number % 1000000);
}

// Example usage:
$number = 1234567;
echo "Number $number in words: "
     . numToWordsRec($number);

?>

Output

Number 1234567 in words: one million two hundred thirty four thousand five hundred sixty seven

Time Complexity: O(Log N)

Auxiliary Space: O(Log N)