Common interview questions

README.md

Those are the 3 most common interview questions...

• Sorting:

  • Bubble, or sinking sort
    • Seeks for the lowers value, swaps in the inner level
      • Means that every iteration would swap values
  • Selection:
    • Seeks for the lowest value, swaps only when found AT the outter level
      • Means that not all iteration would swap values

• Fibonacci

  • You got it :-)

app.php

<?php
require_once "sorting.php";
require_once "fibonacci.php";
/**
 * Just a support function to run the fibonacci
 */
function fibo($total)
{
    $time_start = microtime(true);

    for ($counter = 0; $counter <= $total; $counter++) {
          printf("Fibonacci of %f is: %d\n", $counter, fibonacci($counter));
    }

    $time_end = microtime(true);
    $time     = $time_end - $time_start;
    printf("Fibo spent: %F seconds", $time);

}

$input  = [255,1,22,3,45,5];
$output = [
    'bubble'    => bubble($input),
    'selection' => selection($input),
];
var_dump($output);

fibo(10);

fibonacci.php

<?php
/**
 * If base numbers, 1 or 0, return it
 * Return the value of the current (number - 1) + (current number - 2)
 */
function fibonacci($number)
{
    if ($number === 0 || $number === 1) {
        return $number;
    }

    return fibonacci($number - 1) + fibonacci($number - 2);
}

sorting.php

<?php
/**
 * First loop goes forward
 *  Second loop goes backwards
 *    compares if the previous position is less than or equal the current one
 *      if not, swap positions
 */
function bubble(array $array)
{
    $time_start = microtime(true);
    $n          = count($array);

    for($counter = 1; $counter < $n; $counter++) {
        for ($current = $n -1; $current >= $counter; $current--) {
            $next = $current - 1;
            if ($array[$next] <= $array[$current]) {
                continue;
            }

            $swap            = $array[$next];
            $array[$next]    = $array[$current];
            $array[$current] = $swap;
        }
    }

    $time_end = microtime(true);
    $time     = $time_end - $time_start;

    printf("Bubble spent: %F seconds\n", $time);

    return $array;
}

/**
 * First loop goes forward
 *  Second loop goes forward
 *    compares if the next position is less than or equal the current one
 *      if yes, swap positions
 */
function selection(array $array)
{
    $time_start = microtime(true);
    $n          = count($array);

    for ($current = 0; $current < $n; $current++) {
        $lowestValueIndex = $current;
        $lowestValue      = $array[$current];
        for ($next = $current + 1; $next < $n; $next++) {
            if ($array[$next] < $lowestValue) {
                $lowestValueIndex = $next;
                $lowestValue      = $array[$next];
            }
        }

        $array[$lowestValueIndex] = $array[$current];
        $array[$current]          = $lowestValue;
    }

    $time_end = microtime(true);
    $time     = $time_end - $time_start;

    printf("Selection spent: %F seconds\n", $time);

    return $array;
}