PHP 二分查找(详细)

<?php

// PHP 二分查找

function search($arr, $sea){

 $low = 0; // 确定数组的开始的下标

 $len = count($arr)-1; // 确定数组的最后一下标数组的长度-1

 //echo $len; exit;

 while( $low <= $len ) {

 // 向下取整 2.9 => 2

 $num = floor(($low + $len) / 2);

 //echo $num; echo " ";

 // 中间元素和要查询的比较大小

 // 判读是否是中间的那为数是返回

 if($arr[$num] == $sea){

 return $num;

 }

 // 中间元素比目标大,查找左部

 if($arr[$num] > $sea){

 $len = $num - 1;

 //echo $len; echo " ";

 }

 // 中间元素比目标小,查找右部

 if($arr[$num] < $sea) {

 $low = $num + 1;

 //echo $low; echo " ";

 }

 }

 return false;

}

//使用二分式算法查找数据

$arr = array(1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29);

 // 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

$sch['1'] = search($arr, 27); // 结果 13

 // $num = 7

 // $arr['7'] = 15 < 27 $low = 8; $num = (8 + 14)/2 = 11

 // $arr['11'] = 23 < 27 $low = 12; $num = (12 + 14)/2 = 13

 // $arr['13'] = 27 = 27

$sch['2'] = search($arr, 17); // 结果 8

 // $num = 7

 // $arr['7'] = 15 < 17 $low = $num + 1 = 8; $num = (8 + 14)/2 = 11

 // $arr['11'] = 23 > 17 $len = $num - 1 = 10; $num = (8 + 10)/2 = 9

 // $arr['9'] = 19 > 17 $len = $num - 1 = 8; $num = (8 + 8 )/2 = 8

 // $arr['8'] = 17 = 17

var_dump($sch); // array(2) { [1]=> float(13) [2]=> float(8) }

?>