header('Content-Type: text/html; charset=utf-8;');
$arr = array(2,33,22,1,323,321,28,36,90,123);
sort($arr);
//二分法查找
echo $index = binarySearch($arr,321);
function binarySearch($arr,$key){
 $len = count($arr);
 $mid = -1;
 $start = 0;
 $end  = $len-1;
 while($start<=$end){
 $mid = (int)(($start+$end)/2);
 echo $mid."\n";
 if($arr[$mid] == $key){
  return $mid;
 }else if($arr[$mid] < $key){
  $start = $mid+1;
 }else if($arr[$mid] > $key){
  $end = $mid-1;
 }
 }
}

<?php
//search函數 其中$array為數組，$k為要找的值，$low為查找范圍的最小鍵值，$high為查找范圍的最大鍵值
function search($array, $k, $low=0, $high=0)
{
  if(count($array)!=0 and $high == 0) //判斷是否為第一次調用
  {
    $high = count($array);
  }
  if($low <= $high) //如果還存在剩余的數組元素
  {
    $mid = intval(($low+$high)/2); //取$low和$high的中間值
    if ($array[$mid] == $k) //如果找到則返回
    {
      return $mid;
    }
    elseif ($k < $array[$mid]) //如果沒有找到，則繼續(xù)查找
    {
      return search($array, $k, $low, $mid-1);
    }
    else
    {
      return search($array, $k, $mid+1, $high);
    }
  }
  return -1;
}
$array = array(4,5,7,8,9,10); //測試search函數
echo search($array, 8); //調用search函數并輸出查找結果
?>