daily-coding-problem-1.php

<?php

/**
 * Daily Coding Problem:
 * 
 * Given a list of numbers and a number k, return whether any two numbers from the list add up to k.
 * For example, given [10, 15, 3, 7] and k of 17, return true since 10 + 7 is 17.
 */

function possible($numbers = [], $k) {
    // We don't have enough numbers to add (the minimum numbers are 2).
    if(count($numbers) < 2) {
        return false;
    }

    // We are going to sum the first number (first index) with the other numbers (second index to end) one by one.
    // If the sum of these two numbers is equal to $k, then return true and stop the loop immediatelly.
    for($i = 1; $i < count($numbers); $i++) {
        if($numbers[0] + $numbers[$i] == $k) {
            return true;
        }
    }

    // At this point, the sum of first number (first index) with others numbers does not meet $k.
    // We are going to remove the first number (first index) then start again to match second number (second index) with others index,
    // until we got the $k or until the $numbers is not enough to sum.
    return possible(array_slice($numbers, 1), $k);
}

$numbers = [15, 3, 7, 10];
$k = 17;

echo possible($numbers, $k) ? 'Yes!' . PHP_EOL : 'Nope...' .  PHP_EOL;