PHP Exercises: Reads an integer n and find the number of combinations

Last update on May 27 2025 13:08:44 (UTC/GMT +8 hours)

51. Count Combinations of Digits

Write a PHP program which reads an integer n and find the number of combinations of a,b,c and d (0 ≤ a,b,c,d ≤ 9) where (a + b + c + d) will be equal to n.

Input:
n (1 ≤ n ≤ 50) .

Sample Solution:

PHP Code:

<?php
// Continue reading input until an empty line is encountered
while (($input = trim(fgets(STDIN))) !== '') {
    // Convert the input string to an integer
    $input = intval($input);

    // Initialize a counter for the number of combinations
    $count = 0;

    // Nested loops to iterate over all possible combinations of a, b, c, and d
    for ($i = 0; $i < 10; $i++) {
        for ($j = 0; $j < 10; $j++) {
            for ($k = 0; $k < 10; $k++) {
                for ($l = 0; $l < 10; $l++) {
                    // Check if the sum of a, b, c, and d equals the input
                    if ($i + $j + $k + $l === $input) {
                        // Increment the counter for each valid combination
                        $count++;
                    }
                }
            }
        }
    }

    // Print the number of combinations for the given input
    echo "\nNumber of combinations of a, b, c, and d: ";
    echo $count . "\n";
}

?>

Explanation:

Reading Input:

The program continuously reads input from standard input (STDIN) until an empty line is encountered using fgets(STDIN).

Input Conversion:

Each input string is trimmed of whitespace and converted to an integer using intval($input).

Counter Initialization:

A variable $count is initialized to zero to keep track of the number of valid combinations of digits.

Nested Loops:

Four nested for loops iterate over all possible digit combinations (from 0 to 9) for variables a, b, c, and d:

for ($i = 0; $i < 10; $i++) iterates over possible values for a.
for ($j = 0; $j < 10; $j++) iterates over possible values for b.
for ($k = 0; $k < 10; $k++) iterates over possible values for c.
for ($l = 0; $l < 10; $l++) iterates over possible values for d.

Sum Check:

Inside the innermost loop, the sum of the current values of i, j, k, and l is checked against the input value:

if ($i + $j + $k + $l === $input).

Count Increment:

If the sum matches the input, the counter $count is incremented by one.

Output Results:

After all combinations have been checked, the program prints the number of valid combinations found for the given input.

Output:

Number of combinations of a,b,c and d: 56

Flowchart:

PHP Code Editor:

For more Practice: Solve these Related Problems:

Write a PHP script to count all combinations of four digits that sum to a given integer using nested loops.
Write a PHP function to optimize the counting of digit combinations via dynamic programming techniques.
Write a PHP script to generate and count all unique combinations of four digits that equal a target sum.
Write a PHP script to use recursion to count digit combinations that add up to a specified number.

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