php二分查找二种实现示例

/**
* 二分查找递归解法
* @param type $subject
* @param type $start
* @param type $end
* @param type $key
* @return boolean
*/
function binarySearch_r($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);
}
}

/**
* 二分查找的非递归算法
* @param type $subject
* @param type $n
* @param type $key
*/
function binarySearch_nr($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, $key)
{
/**
* 取中值算法1 取中值 不用 ($low+$high)/2的方式是因为 防止low和high较大时候，产生溢出….
*/
//return round($low + ($high – $low) / 2);

/**
* 经过改进的插值算法求中值，当数值分布均匀情况下，再降低算法复杂度到lglgN
* 取中值算法2
*/
return round( (($key – $subject[$low]) / ($subject[$high] – $subject[$low])*($high-$low) ) );
}