PHP array key-value conversion speed competition

$arr = range(1, 1000000);

// 使用 array_flip()
$start = microtime(true);
$flipped = array_flip($arr);
$end = microtime(true);
$time_array_flip = $end - $start;

// 使用 array_combine()
$keys = range('a', 'z');
$start = microtime(true);
$combined = array_combine($keys, $arr);
$end = microtime(true);
$time_array_combine = $end - $start;

// 使用 array_map()
$start = microtime(true);
$mapped = array_map(function($x) { return [$x, $x]; }, $arr);
$end = microtime(true);
$time_array_map = $end - $start;

// 使用 foreach() 和 array_keys()
$start = microtime(true);
$flipped = [];
$keys = array_keys($arr);
foreach ($keys as $key) { $flipped[$key] = $arr[$key]; }
$end = microtime(true);
$time_foreach = $end - $start;

// 使用自定义循环
$start = microtime(true);
$flipped = [];
for ($i = 0; $i < count($arr); $i++) { $flipped[$arr[$i]] = $arr[$i]; }
$end = microtime(true);
$time_custom = $end - $start;

// 显示结果
echo "array_flip(): $time_array_flip s\n";
echo "array_combine(): $time_array_combine s\n";
echo "array_map(): $time_array_map s\n";
echo "foreach() + array_keys(): $time_foreach s\n";
echo "自定义循环: $time_custom s\n";