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) }

巴特西