PHP. Собеседование в вопросах и ответах

<?php
define('NUM', 1000000);
$start = microtime(true);
for ($i = 0; $i < NUM; $i++);
$for_time = microtime(true) - $start;

$some_str = "Hello world!";

echo "For loop time: " . round($for_time, 3) . " sec\n";

$start = microtime(true);
for ($i = 0; $i < NUM; $i++);
echo "Empty stmt time (should be 0): " . round(microtime(true) - $start - $for_time, 3) . " sec\n";;

$start = microtime(true);
for ($i = 0; $i < NUM; $i++) {
	"hello world $for_time $i $for_time $i $for_time $i $some_str $some_str";
}
echo "Double quotes: " . round(microtime(true) - $start - $for_time, 3) . " sec\n";

$start = microtime(true);
for ($i = 0; $i < NUM; $i++) {
	'hello world ' . $for_time . ' ' . $i . ' ' . $for_time .' ' . $i . ' ' . $for_time . ' ' . $i . ' ' . $some_str . ' ' . $some_str;
}
echo "Single quotes: " . round(microtime(true) - $start - $for_time, 3) . " sec\n";

$ php bench.php 
For loop time: 0.097 sec
Empty stmt time (should be 0): -0.005 sec
Double quotes: 2.183 sec
Single quotes: 2.891 sec

<?php

$iterations = 100001;

$arr = array('h', 'e', 'l', 'l', 'o');
$t1 = microtime(true);
for ($i = 0; $i < $iterations; $i++) {
	$arr = reverse1($arr);
}
$t1 = microtime(true) - $t1;
var_dump($arr);
var_dump($t1);

$arr = array('h', 'e', 'l', 'l', 'o');
$t2 = microtime(true);
for ($i = 0; $i < $iterations; $i++) {
	$arr = reverse2($arr);
}
$t2 = microtime(true) - $t2;

var_dump($arr);
var_dump($t2);

function reverse1($arr) {
	for ($i = 0; $i < floor(count($arr)/2); $i++)
	{
		$tmp = $arr[$i];
		$arr[$i] = $arr[count($arr)-$i-1];
		$arr[count($arr)-$i-1] = $tmp;
	}
	return $arr;
}

function reverse2($arr) {
	$c = count($arr);
	for ($i = 0; $i < floor($c/2); $i++)
	{
		$tmp = $arr[$i];
		$arr[$i] = $arr[$c-$i-1];
		$arr[$c-$i-1] = $tmp;
	}
	return $arr;
}

array
  0 => string 'o' (length=1)
  1 => string 'l' (length=1)
  2 => string 'l' (length=1)
  3 => string 'e' (length=1)
  4 => string 'h' (length=1)

float 2.8682391643524

array
  0 => string 'o' (length=1)
  1 => string 'l' (length=1)
  2 => string 'l' (length=1)
  3 => string 'e' (length=1)
  4 => string 'h' (length=1)

float 1.7087500095367