性能分析:从运行性能上分析，看看下面的测试代码：
$test=array();
for($run=0; $run<10000; $run++)
$test[]=rand(0,100);
$time=microtime(true);
$out = array_unique($test);
$time=microtime(true)-$time;
echo 'Array Unique: '.$time."\n";
$time=microtime(true);
$out=array_keys(array_flip($test));
$time=microtime(true)-$time;
echo 'Keys Flip: '.$time."\n";
$time=microt...