awrk_test.php

<?php

// Problem 1
function reverse($x) {
    $x = intval($x);
    if ($x < 0) {
        return false;
    }

    $reversedInt = 0;
    $copyX = $x;
    
    while ($x > 0) {
        $remainder = $x % 10;
        $x = (int)($x/10);

        $reversedInt = ($reversedInt * 10) + $remainder;
        
    }
    
    return $copyX === $reversedInt;
}



// Problem 2
function findTheNum($arr) {
    $map = [];

    foreach($arr as $item) {
        if (!array_key_exists($item, $map)) {
            $map[$item] = 0;
        }

        $map[$item]++;
    }

    foreach($map as $key => $value) {
        if ($value === 1) {
            return $key;
        }
    }
}


// Problem 3
function exchange($bills) {
    $notes = [
        5 => 0,
        10 => 0,
        20 => 0
    ];


    foreach($bills as $bill) {
        if ($bill === 5) {
            $notes[5]++;
        } elseif($bill === 10) {
            if ($notes[5] >= 1) {
                $notes[5]--;
                $notes[10]++;
            } else {
                return false;
            } 
        } elseif($bill === 20) {
            if ($notes[5] >= 1 && $notes[10] >= 1) {
                $notes[5]--;
                $notes[10]--;
                $notes[20]++;
            } else {
                return false;
            }
        }
    }

    return true;
}