php二分查找二种实现示例

php二分查找示例

二分查找常用写法有递归和非递归，在寻找中值的时候，可以用插值法代替求中值法。
当有序数组中的数据均匀递增时，采用插值方法可以将算法复杂度从中值法的lgN减小到lglgN

复制代码 代码如下:

function binarySearch_r($subject, $start, $end, $key)
{

 if ( $start >= $end ) return FALSE;
 $mid = getMidKey($subject, $start, $end, $key);
 if ( $subject[$mid] == $key ) return $mid;
 if ( $key > $subject[$mid] ) {
  return binarySearch($subject, $mid, $end, $key);
 }
 if ( $key <= $subject[$mid] ) {
  return binarySearch($subject, $start, $mid, $key);
 }
}

function binarySearch_nr($subject, $n, $key)
{
 $low = 0;
 $high = $n;
 while ( $low <= $high ) {
  $mid = getMidKey($subject, $low, $high, $key);
  if ( $subject[$mid] == $key ) return $mid;
  if ( $subject[$mid] < $key ) {
   $low = $mid + 1;
  }
  if ( $subject[$mid] > $key ) {
   $high = $mid - 1;
  }
 }
}
function getMidKey($subject, $low, $high, $key)
{
 
 //return round($low + ($high - $low) / 2);

 
 return round( (($key - $subject[$low]) / ($subject[$high] - $subject[$low])*($high-$low) ) );
}