常见查找算法之php, js,python版

常用算法

>>>1. 顺序查找, 也叫线性查找, 它从第一个记录开始, 挨个进行对比, 是最基本的查找技术

javaScript 版顺序查找算法:

 // 顺序查找(线性查找) 只做找到即返回

 // javaScript 版

 function search(data,needle)

 {

     for(var i=0;i<data.length;i++)

     {

         if(data[i] == needle && typeof data[i] == typeof needle)

         {

             return i;

         }

     }

     return false;

 }

 var data = [100,10,2,7,8,6];

 console.log(search(data,7));//

 console.log(search(data,'7'));// false

php版顺序查找算法:

 <?php

 // php版

 function search($data,$needle)

 {

     $data_len = count($data);

     for($i=0;$i<$data_len;$i++)

     {

         if($data[$i] === $needle) return $i;

     }

     return false;

 }

 $data = [100,10,2,7,8,6];

 var_dump(search($data,7));// int(3)

 var_dump(search($data,'7'));// bool(false)

python3 版顺序查找算法:

 # python3 版本

 def search(data,needle) :

     dataLen = len(data)

     for i in range(dataLen) :

         if data[i] == needle and type(data[i]) == type(needle) : return i

     return False

 data = [100,10,2,7,8,6]

 print(search(data,7))   #

 print(search(data,'')) # False

 print(search(data,6))   #

>>>二分找查, 折半查找

核心思想:

1. 用low , high , middle 表示待查找区间的 下界, 上界,中间 的坐标

2. 取中间位置 middle = floor((low+high)/2)

3. 用给定值与 中间位置的值 作比较

等于: 查找成功

大于: 待查数据在区间的后半段  设low 为 middle+1

小于: 待查数据在区间的前半段  设high 为 middle-1

4.数据是排序好的

5.直到越界 (low>high) 查找失败, 结束

PHP版二分查找算法:

 <?php

 // 二分法 折半查找 PHP版

 $data_list = [1,2,4,5,5,6,10,12];

 function bisearch($data_list,$needle)

 {

     $low = 0;

     $high = count($data_list)-1;

     if($data_list[$low] == $needle) return $low;

     if($data_list[$high] == $needle) return $high;

     while($high>=$low)

     {

         $middle = floor(($low+$high)/2);

         if($needle == $data_list[$middle])

         {

             return $middle;

         }elseif($needle>$data_list[$middle])

         {

             $low = $middle+1;

         }else{

             $high = $middle-1;

         }

     }

     return false;

 }

 print_r(bisearch($data_list,10)); //

 print_r(bisearch($data_list,5));  //

 print_r(bisearch($data_list,13)); // false

python 3版 二分查找算法:

 import math

 # python3 版二分查找算法

 def bisearch(data_list,needle) :

     low,high = 0,len(data_list)-1

     if needle == data_list[low] :  return low

     if needle == data_list[high] : return high

     while high>=low :

         middle = math.floor((high+low)/2)

         if needle == data_list[middle] :  return middle

         elif needle > data_list[middle] : low = middle+1

         else : high = middle-1

     return False

 data_list = [1,2,4,5,5,6,10,12]

 print(bisearch(data_list,10));   #

 print(bisearch(data_list,5));    #

 print(bisearch(data_list,13));   # False

javaScript 版二分查找算法:

 // js 版二分查找

 function bisearch(data_list,needle)

 {

     var low = 0,high = data_list.length-1

     if (needle == data_list[low] ) return low

     if (needle == data_list[high]) return high

     while (high>=low)

     {

         var middle = Math.floor((low+high)/2)

         if(needle == data_list[middle])

         {

             return middle

         }else if(needle>data_list[middle])

         {

             low = middle + 1

         }else{

             high = middle - 1

         }

     }

     return false

 }

 data_list = [1,2,4,5,5,6,10,12]

 console.log(bisearch(data_list,10));   //

 console.log(bisearch(data_list,5));    //

 console.log(bisearch(data_list,13));   // False

>>> 插值查找 (由二分查找改进)

二分查找的公式:

middle = (low+high)/2    => low+(1/2)*(high-low)

插值查找的公式由上面演变, 主要改进的是二分之一部分:

middle = low+((needle-data[low])/(data[high]-data[low]))*(high-low)

对二分查找跟插值查找的一个说明:

插值查找对于公布均匀的数据, 速度比二分查找快(插值查找次数少),例如对下面这类数据

$data = [1,2,3,6,7,9,10,11,...]

对于分布不均匀的数据, 二分查找要比插值查找快 例如下:

$data = [4,100,300,685,3452,...]

PHP版 插值查找算法:

 <?php

 // 二分查找优化(插值查找) PHP版

 $data_list = [1,2,4,5,5,6,10,12];

 function interpolation($data_list,$needle)

 {

     $low = 0;

     $high = count($data_list)-1;

     if($data_list[$low] == $needle) return $low;

     if($data_list[$high] == $needle) return $high;

     while($high>=$low)

     {

         $middle = floor($low+(($needle-$data_list[$low])/($data_list[$high]-$data_list[$low]))*($high-$low));

         if($needle == $data_list[$middle])

         {

             return $middle;

         }elseif($needle>$data_list[$middle])

         {

             $low = $middle+1;

         }else{

             $high = $middle-1;

         }

     }

     return false;

 }

 print(interpolation($data_list,10)); //

 print(interpolation($data_list,5));  //

 print(interpolation($data_list,13)); // false

 $index = interpolation($data_list,10);

 echo $data_list[$index];//

 /*

  注: 1.floor 返回的是浮点数 如 6 类型为float

      2.false 用print,echo 输出是空字符串

 */

python3版 插值查找算法:

 import math

 # python3 插值查找算法

 def interpolation(data_list,needle) :

     low,high = 0,len(data_list)-1

     if needle == data_list[low] :  return low

     if needle == data_list[high] : return high

     while high>=low :

         middle = math.floor(

             low+

             ((needle-data_list[low])/(data_list[high]-data_list[low]))*

             (high-low)

         )

         if needle == data_list[middle] :  return middle

         elif needle > data_list[middle] : low = middle+1

         else : high = middle-1

     return False

 data_list = [1,2,4,5,5,6,10,12]

 print(interpolation(data_list,10));   #

 print(interpolation(data_list,5));    #

 print(interpolation(data_list,13));   # False

js 版插值查找算法:

 // js版 插值查找算法

 function interpolation(data_list,needle)

 {

     var low = 0,high = data_list.length-1

     if (needle == data_list[low] ) return low

     if (needle == data_list[high]) return high

     while (high>=low)

     {

         var middle = Math.floor(

             low+((needle-data_list[low])/(data_list[high]-data_list[low]))*

             (high-low)   

         )

         if(needle == data_list[middle])

         {

             return middle

         }else if(needle>data_list[middle])

         {

             low = middle + 1

         }else{

             high = middle - 1

         }

     }

     return false

 }

 data_list = [1,2,4,5,5,6,10,12]

 console.log(interpolation(data_list,10));   //

 console.log(interpolation(data_list,5));    //

 console.log(interpolation(data_list,13));   // False

小结:

以上有php,python,js 版常见的查找算法:

1. 顺序(线性) 查找

2. 二分查找 (折半查找)

3. 插值查找 (二分查找优化 适用于分布均匀的数据)

4. 前提是数据排好序, 顺序