Example of PHP binary search algorithm [Recursive and non-recursive methods]

This article describes the PHP binary search algorithm. Share it for your reference, as follows:

binarySearch

The method used for binary search is easier to understand, taking arrays as an example:

① First take the value floor((low+top)/2) in the middle of the array,

② Then compare with the number you want to find. If it is larger than the intermediate value, replace the first value with the next position in the middle position and continue the first step of operation. If it is smaller than the intermediate value, replace the tail value with the previous position in the middle position and continue the first step of operation.

③ Repeat the second step until the target number is found

For example, look up the number 23 from 1, 3, 9, 23, 54,

The first position is 0, the tail position is 4, the middle position is 2. The value is 9, which is smaller than 23, and the first position is updated to 2+1, that is, 3; then the middle position is (3+4)/2=3, the value is 23, and the same is found

// Non-recursive algorithm:// $target is the target to be found $arr is an array already sortedfunction binary(&$arr,$low,$top,$target){
    while($low <= $top){
// Since PHP has decimal numbers, it is rounded downward, but it can also be added, and the array will also be rounded.      $mid = floor(($low+$top)/2);
      echo $mid."<br>";
      if($arr[$mid]==$target){
        return $arr[$mid];
      }elseif($arr[$mid]<$target){
        $low = $mid+1;
      }else{
        $top = $mid-1;
      }
    }
    return -1;
}

// Recursive algorithm:function binaryRecursive(&$arr,$low,$top,$target){
    if($low<=$top){
      $mid = floor(($low+$top)/2);
      if($mid==$target){
        return $arr[$mid];
      }elseif($arr[$mid]<$target){
        return binaryRecursive($arr,$mid+1,$top,$target);
      }else{
        return binaryRecursive($arr,$low,$top-1,$target);
      }
    }else{
      return -1;
    }
}

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I hope this article will be helpful to everyone's PHP programming.