Binary search algorithm

The premise of binary search algorithm:

1, for the index array;

2, for arrays that are already lined up.

Code Demo:

//function function: Find data from position $begin start to position $end in array $arr $sfunctionBinary_search ($arr,$s,$begin,$end){    $mid= Floor(($begin+$end)/2);//Locate the middle position    $mid _value=$arr[$mid];//gets the value of the middle item    if($mid _value==$s)    {        return true; }Else if($mid _value>$s)    {        if($begin>$mid-1)//if the starting position is larger than the end position, it means that it must not be found.        {            return false; }        //the middle item is bigger than the $s to find, go to the left to find it:        $re= Binary_search ($arr,$s,$begin,$mid-1); }Else    {        if($mid+1 >$end)//if the starting position is larger than the end position, it means that it must not be found.        {            return false; }        //the middle item is smaller than the $s to be searched, go to the right to find it;        $re= Binary_search ($arr,$s,$mid+1,$end); }    return $re;}

test code:

 <? php   $a  = array  ( 1,3,11,18,19,22,25,33,34,38,44,55,56,58  $search  = 35; //  The number to find   $len  = count  (  $a ); //  number, natural, maximum subscript is len-1//use the Binary_search () function to find len-1  $search  $v 1  = Binary_search ( $a ,  $search , 0, $len  -1 echo  "The result is:"  var_dump  ( $v 1 ); 

Test results:

· The result is: BOOL (false)

A little explanation of the efficiency (performance) problem of the binary lookup algorithm:

1000 data, about 10 times to find out;

100 complete data, about 20 times to find out;

1 billion data, about 30 times to find out;

4 billion data, about 32 times to find out.

Binary search algorithm