PHP binary Search Algorithm example analysis PHP tips

This article mainly introduces PHP binary (binary) search algorithm, combined with the case of the form of a more detailed analysis of the PHP binary (binary) search algorithm concept, principle, implementation and use method, and with a PHP binary (binary) search algorithm class for everyone to reference, the need for friends can refer to the next

The example of PHP binary (binary) lookup algorithm is described in this paper. Share to everyone for your reference, as follows:

The binary query is only applicable to arrays, strings, etc. that have been sorted in a positive or reverse order;

Algorithm:

Takes the middle position of the array first, without the middle position, then takes down the whole;

From the middle of the binary, size judgment, into the first half or the second half of the paragraph;

Make the same binary query for the first half or the second half of the paragraph,

Stop until the matching character is queried (this example uses break, if placed in a function, return)

PHP implements the following code:

<?php$arr = Array (1,2,3,4,5,6,7,8,9,10);//Array $key = 4;//the keyword to query $low = 0;//start bit flag $high = count ($arr);//The flag of the terminating bit while ($  Low <= $high) {//The condition at which the query begins to end $mid = Floor (($low + $high)/2);//Intermediate position calculation, rounding down if ($arr [$mid] = = $key) {//query successful echo $arr [$mid]; break;//end of this page, function can return}elseif ($arr [$mid] > $key) {//Query the first half, move the end flag to the middle of the previous position $high = $mid-1;} else{//The second half of the query, move the start position to the middle position of the latter $low = $mid + 1;}} /* Run result:4*/?>

Add: Binary (binary) find the algorithm class:

/** * description:php The class that implements the binary lookup algorithm * @author wzy */class binary_search{public  $arr;  public $key;  function __construct ($arr, $key) {    //the array initialized here is already an ordered array    $this->arr= $arr;    $this->key= $key;  }  function BinarySearch () {    $start =0;    $end =count ($this->arr)-1;    while ($start <= $end) {      //mid can be either an integer or an integer      $mid =ceil ($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;}}}  

You may also encounter this situation where the elements in the array have duplicate data and need to return the position of the first element in the repeating data, for example

$arr =array (1,2,3,4,5,6,6,6,6,7,8);

The position returned when looking for the 6 element should be 5, not the other (the subscript starts with a 0 count), so it needs to be judged in the returned mid, with the following code:

/** * description:php The class that implements the binary lookup algorithm * @author wzy */class binary_search{public  $arr;  public $key;  function __construct ($arr, $key) {    //the array initialized here is already an ordered array    $this->arr= $arr;    $this->key= $key;  }  function BinarySearch () {    $start =0;    $end =count ($this->arr)-1;    while ($start <= $end) {      //mid can be either an integer or an integer      $mid =ceil ($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 = $mid-1;      } else{        //Returns the first matching element for        ($i = $mid-1; $i >=0; $i-) {          if ($this->arr[$i]== $this->key) {            $ Mid= $i;          } else{break            ;          }        }        return $mid;}}}  

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