常见查找算法之php, js,python版

Posted 2020-10-19 Dong_Alex

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:

 1 // 顺序查找(线性查找) 只做找到即返回
 2  
 3 // javaScript 版
 4  
 5 function search(data,needle)
 6  
 7 {
 8  
 9     for(var i=0;i<data.length;i++)
10  
11     {
12  
13         if(data[i] == needle && typeof data[i] == typeof needle)
14  
15         {
16  
17             return i;
18  
19         }
20  
21     }
22  
23     return false;
24  
25 }
26  
27  
28 var data = [100,10,2,7,8,6];
29  
30 console.log(search(data,7));// 3
31  
32 console.log(search(data,\'7\'));// false

 php版顺序查找算法:

 1 <?php
 2  
 3 // php版
 4  
 5 function search($data,$needle)
 6  
 7 {
 8  
 9     $data_len = count($data);
10  
11     for($i=0;$i<$data_len;$i++)
12  
13     {
14  
15         if($data[$i] === $needle) return $i;
16  
17     }
18  
19     return false;
20  
21 }
22  
23  
24  
25 $data = [100,10,2,7,8,6];
26  
27 var_dump(search($data,7));// int(3)
28  
29 var_dump(search($data,\'7\'));// bool(false)

 python3 版顺序查找算法:

 1 # python3 版本
 2  
 3 def search(data,needle) :
 4  
 5     dataLen = len(data)
 6  
 7     for i in range(dataLen) :
 8  
 9         if data[i] == needle and type(data[i]) == type(needle) : return i
10  
11     return False
12  
13  
14 data = [100,10,2,7,8,6]
15  
16 print(search(data,7))   # 3
17  
18 print(search(data,\'7\')) # False
19  
20 print(search(data,6))   # 5

 >>>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:

 1 <?php
 2  
 3 // 二分法 折半查找 PHP版
 4  
 5 $data_list = [1,2,4,5,5,6,10,12];
 6  
 7 function bisearch($data_list,$needle)
 8  
 9 {
10  
11     $low = 0;
12  
13     $high = count($data_list)-1;
14  
15     if($data_list[$low] == $needle) return $low;
16  
17     if($data_list[$high] == $needle) return $high;
18  
19     while($high>=$low)
20  
21     {
22  
23         $middle = floor(($low+$high)/2);
24  
25         if($needle == $data_list[$middle])
26  
27         {
28  
29             return $middle;
30  
31         }elseif($needle>$data_list[$middle])
32  
33         {
34  
35             $low = $middle+1;
36  
37         }else{
38  
39             $high = $middle-1;
40  
41         }
42  
43     }
44  
45     return false;
46  
47 }
48  
49  
50  
51 print_r(bisearch($data_list,10)); // 6
52  
53 print_r(bisearch($data_list,5));  // 3
54  
55 print_r(bisearch($data_list,13)); // false

 python 3版 二分查找算法:

 1 import math
 2  
 3 # python3 版二分查找算法
 4  
 5 def bisearch(data_list,needle) :
 6  
 7     low,high = 0,len(data_list)-1
 8  
 9     if needle == data_list[low] :  return low
10  
11     if needle == data_list[high] : return high
12  
13     while high>=low :
14  
15         middle = math.floor((high+low)/2)
16  
17         if needle == data_list[middle] :  return middle
18  
19         elif needle > data_list[middle] : low = middle+1
20  
21         else : high = middle-1
22  
23     return False
24  
25  
26  
27 data_list = [1,2,4,5,5,6,10,12]
28  
29 print(bisearch(data_list,10));   # 6
30  
31 print(bisearch(data_list,5));    # 3
32  
33 print(bisearch(data_list,13));   # False

javaScript 版二分查找算法:

 1 // js 版二分查找
 2  
 3 function bisearch(data_list,needle)
 4  
 5 {
 6  
 7     var low = 0,high = data_list.length-1
 8  
 9     if (needle == data_list[low] ) return low
10  
11     if (needle == data_list[high]) return high
12  
13     while (high>=low)
14  
15     {
16  
17         var middle = Math.floor((low+high)/2)
18  
19         if(needle == data_list[middle])
20  
21         {
22  
23             return middle
24  
25         }else if(needle>data_list[middle])
26  
27         {
28  
29             low = middle + 1
30  
31         }else{
32  
33             high = middle - 1
34  
35         }
36  
37     }
38  
39     return false
40  
41 }
42  
43 data_list = [1,2,4,5,5,6,10,12]
44  
45 console.log(bisearch(data_list,10));   // 6
46  
47 console.log(bisearch(data_list,5));    // 3
48  
49 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:

 1 <?php
 2  
 3 // 二分查找优化(插值查找) PHP版
 4  
 5 $data_list = [1,2,4,5,5,6,10,12];
 6  
 7 function interpolation($data_list,$needle)
 8  
 9 {
10  
11     $low = 0;
12  
13     $high = count($data_list)-1;
14  
15     if($data_list[$low] == $needle) return $low;
16  
17     if($data_list[$high] == $needle) return $high;
18  
19     while($high>=$low)
20  
21     {
22  
23         $middle = floor($low+(($needle-$data_list[$low])/($data_list[$high]-$data_list[$low]))*($high-$low));
24  
25         if($needle == $data_list[$middle])
26  
27         {
28  
29             return $middle;
30  
31         }elseif($needle>$data_list[$middle])
32  
33         {
34  
35             $low = $middle+1;
36  
37         }else{
38  
39             $high = $middle-1;
40  
41         }
42  
43     }
44  
45     return false;
46  
47 }
48  
49  
50  
51 print(interpolation($data_list,10)); // 6
52  
53 print(interpolation($data_list,5));  // 3
54  
55 print(interpolation($data_list,13)); // false
56  
57  
58  
59 $index = interpolation($data_list,10);
60  
61 echo $data_list[$index];// 10
62  
63  
64 /*
65  
66  注: 1.floor 返回的是浮点数 如 6 类型为float
67  
68      2.false 用print,echo 输出是空字符串
69  
70 */

python3版 插值查找算法:

 1 import math
 2  
 3 # python3 插值查找算法
 4  
 5 def interpolation(data_list,needle) :
 6  
 7     low,high = 0,len(data_list)-1
 8  
 9     if needle == data_list[low] :  return low
10  
11     if needle == data_list[high] : return high
12  
13     while high>=low :
14  
15         middle = math.floor(
16  
17             low+
18  
19             ((needle-data_list[low])/(data_list[high]-data_list[low]))*
20  
21             (high-low)
22  
23         )
24  
25         if needle == data_list[middle] :  return middle
26  
27         elif needle > data_list[middle] : low = middle+1
28  
29         else : high = middle-1
30  
31     return False
32  
33  
34  
35 data_list = [1,2,4,5,5,6,10,12]
36  
37 print(interpolation(data_list,10));   # 6
38  
39 print(interpolation(data_list,5));    # 3
40  
41 print(interpolation(data_list,13));   # False

js 版插值查找算法:

 1 // js版 插值查找算法
 2  
 3 function interpolation(data_list,needle)
 4  
 5 {
 6  
 7     var low = 0,high = data_list.length-1
 8  
 9     if (needle == data_list[low] ) return low
10  
11     if (needle == data_list[high]) return high
12  
13     while (high>=low)
14  
15     {
16  
17         var middle = Math.floor(
18  
19             low+((needle-data_list[low])/(data_list[high]-data_list[low]))*
20  
21             (high-low)   
22  
23         )
24  
25         if(needle == data_list[middle])
26  
27         {
28  
29             return middle
30  
31         }else if(needle>data_list[middle])
32  
33         {
34  
35             low = middle + 1
36  
37         }else{
38  
39             high = middle - 1
40  
41         }
42  
43     }
44  
45     return false
46  
47 }
48  
49 data_list = [1,2,4,5,5,6,10,12]
50  
51 console.log(interpolation(data_list,10));   // 6
52  
53 console.log(interpolation(data_list,5));    // 3
54  
55 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