PHP half (bisection) search algorithm example analysis
This article mainly introduces the PHP half (two-point) search algorithm. It analyzes the concept, principle, implementation and usage of the PHP half-half (two-point) search algorithm in detail in the form of examples. It also comes with a PHP half (two-point) search algorithm. ) Search algorithm class for your reference. Friends who need it can refer to
. The example in this article describes the PHP half (bisection) search algorithm. Share it with everyone for your reference, the details are as follows:
Half query is only applicable to arrays, strings, etc. that have been sorted in positive or reverse order;
Algorithm:
First take the middle position of the array, if there is no middle position, then round down;
Fold it in half from the middle, judge the size, and enter the first half or the second half;
then Perform the same half-and-half query on the first half or the second half,
will not stop until the matching character is found (in this example, break is used, if it is placed in a function, just return)
The code implemented by php is as follows:
<?php
$arr = array(1,2,3,4,5,6,7,8,9,10);//数组
$key = 4;//要查询的关键字
$low = 0;//开始位的标志
$high = count($arr);//终止位的标志
while($low <= $high){//查询开始结束的条件
$mid = floor(($low + $high)/2);//进行中间位置计算，向下取整
if($arr[$mid] == $key){//查询成功
echo $arr[$mid];
break;//结束本页执行，函数可用return
}elseif($arr[$mid] > $key){ //查询前半段，把结束标志移到中间位置前一位
$high = $mid - 1;
}else{ //查询后半段，把开始位置移到中间位置的后一位
$low = $mid + 1;
}
}
/*
运行结果：4
*/
?>##Additional: Halving (bisection) search algorithm class:
/**
* Description:php实现二分查找算法的类
* @author wzy
*/
class binary_search{
public $arr;
public $key;
function __construct($arr,$key){
//这里初始化的数组已经是有序数组
$this->arr=$arr;
$this->key=$key;
}
function binarysearch(){
$start=0;
$end=count($this->arr)-1;
while($start<=$end){
//mid的取值可以为上整数或者下整数
$mid=ceil(($start+$end)/2);
//$mid=($start+$end)>>1;
//$mid=intval(($start+$end)/2);
if($this->arr[$mid]<$this->key){
$start=$mid+1;
}else if($this->arr[$mid]>$this->key){
$end=$mid-1;
}else{
return $mid;
}
}
}
}$arr=array(1,2,3,4,5,6,6,6,6,7,8);
/**
* Description:php实现二分查找算法的类
* @author wzy
*/
class binary_search{
public $arr;
public $key;
function __construct($arr,$key){
//这里初始化的数组已经是有序数组
$this->arr=$arr;
$this->key=$key;
}
function binarysearch(){
$start=0;
$end=count($this->arr)-1;
while($start<=$end){
//mid的取值可以为上整数或者下整数
$mid=ceil(($start+$end)/2);
//$mid=($start+$end)>>1;
//$mid=intval(($start+$end)/2);
if($this->arr[$mid]<$this->key){
$start=$mid+1;
}else if($this->arr[$mid]>$this->key){
$end=$mid-1;
}else{
//返回第一个匹配的元素
for($i=$mid-1;$i>=0;$i--){
if($this->arr[$i]==$this->key){
$mid=$i;
}else{
break;
}
}
return $mid;
}
}
}
}# #
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