一个无聊男人的疯狂《数据结构与算法分析-C++描述》学习笔记 用C++/lua/python/bash的四重实现（4）二分搜索算法

一个无聊男人的疯狂《数据结构与算法分析-C++描述》学习笔记 用C++/lua/python/bash的四重实现（4）二分搜索算法

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<<Data Structures and Algorithm Analysis in C++>>

--《数据结构与算法分析c++描述》 Mark Allen Weiss著 人民邮电大学出版 中文版第44面，图2-9二分搜索算法

二分搜索是很著名也很实用的算法，在排序中查找的速度从算法分析角度来说已经是最快的了。O(logN)

这里费了点心，将bash都实现了，扭曲啊，扭曲，光是传递一个数组参数都折腾了半天，最后还是通过所谓的间接引用然后用for重新赋值才实现我想要的数组，再次认为bash的算法描述语法混乱不堪。。。。其实bash只有命令调用的语法好用而已（个人见解），但是碰到我这样无聊的人，偏偏要用bash去实现算法。。。那就只能稍微偷点懒了，用了bash的C语言语法部分。

以下4个算法都是一样的，测试时为了统一结果，消除因为cpp,python数组从0开始，lua,bash数组从1开始的问题，测试时，cpp,python从-1开始测试。最后测试完成的结果完全一致，来个有意思的截图：

我编码的时候平铺4个putty窗口，正好占满我的19寸屏：）

从左自右依次是cpp,lua,python,bash。


以下是源代码：

CPP:

1
#include
<stdio.h>

2 #include
<stdlib.h>

3 #include
<vector>

4 #include
<iostream>

5 using namespace std;

6 template<typename T>

7 int binarySearch(const vector<T> &a, const T &x, int& aiTimes)

8 {

9 int low = 0;

10 int high = a.size() - 1;

11

12 while(low <= high)

13 {

14 ++aiTimes;

15 int mid = (low + high) / 2;

16

17 if(a[mid] < x)

18 {

19 low
= mid + 1;

20 }

21 else if(a[mid]
> x)

22 {

23 high
= mid - 1;

24 }

25 else

26 {

27 return mid;

28 }

29 }

30

31 return -1;

32 }

33

34 int main(int argc, char*
argv[])

35 {

36 vector<int> lveci;

37 lveci.resize(100);

38 for(int i
= 0; i < 100;
++i)

39 {

40 lveci[i]
= i;

41 }

42

43 int liTimes = 0;

44 cout <<
binarySearch(lveci, -1, liTimes);

45 cout <<"/tcost:" <<liTimes <<endl;

46 liTimes = 0;

47 cout << binarySearch(lveci,
0, liTimes);

48 cout <<"/tcost:" <<liTimes <<endl;

49 liTimes = 0;

50 cout <<
binarySearch(lveci, 1, liTimes);

51 cout <<"/tcost:" <<liTimes <<endl;

52 liTimes = 0;

53 cout <<
binarySearch(lveci, 2, liTimes);

54 cout <<"/tcost:" <<liTimes <<endl;

55 liTimes = 0;

56 cout <<
binarySearch(lveci, 100, liTimes);

57 cout <<"/tcost:"<<liTimes <<endl;

58

59

60

61 exit(0);

62 }

63

LUA:

1
#!/usr/bin/env
lua

2 function binarySearch(a,
v)

3 low = 1

4 high = #a

5

6 times = 0

7 while(low <= high) do

8 times
= times + 1

9 mid
= math.floor(( low + high) / 2)

10 if a[mid] < v then

11 low
= mid + 1

12 elseif a[mid] > v then

13 high
= mid - 1

14 else

15 return mid,times

16 end

17 end

18

19 return -1,times

20 end

21

22 -- test code

23 array = {}

24 for i=1,100 do

25 array[i] = i

26 end

27

28 print(binarySearch(array,
0))

29 print(binarySearch(array,
1))

30 print(binarySearch(array,
2))

31 print(binarySearch(array,
3))

32 print(binarySearch(array,
101))

33

PYTHON:

1
#!/usr/bin/env
python

2

3 def binarySearch(a, v):

4 low = 0

5 high =
len(a) - 1

6 times = 0

7

8 while low <= high:

9 times
+= 1

10 mid
= (low + high) // 2

11

12 if v > a[mid]:

13 low
= mid + 1

14 elif v < a[mid]:

15 high
= mid - 1

16 else:

17 return mid,times

18

19 return -1,times

20

21 array = range(100)

22 print binarySearch(array, -1)

23 print binarySearch(array, 0)

24 print binarySearch(array, 1)

25 print binarySearch(array, 2)

26 print binarySearch(array,
100)

27

28

BASH:

1
#!/usr/bin/env
bash

2

3

4 binarySearch()

5 {

6 v=$2

7 an="$1[@]"

8 a=${!an}

9 for i in $a

10 do

11 ar[i]=$i

12 done

13 low=1

14 high=${#ar[*]}

15 (( times=0 ))

16

17 while (( low
<= high ))

18 do

19 (( ++times ))

20 (( mid=(low+high)/2 ))

21 #echo -n " mid="$mid

22 #echo -n " ar[mid]="${ar[mid]}

23 if (( v
> ar[mid] ))

24 then

25 (( low = mid + 1 ))

26 elif (( v
< ar[mid] ))

27 then

28 (( high = mid - 1 ))

29 else

30 #echo -e "/nTimes="$times

31 return $mid

32 fi

33 done

34

35 #echo -e "/nTimes="$times

36 return -1

37 }

38

39 for ((i=1; i<= 100; ++i))

40 do

41 (( array[i] = i
))

42 done

43

44 binarySearch array 0

45 echo -e
"$?/t$times"

46 binarySearch array 1

47 echo -e
"$?/t$times"

48 binarySearch array 2

49 echo -e
"$?/t$times"

50 binarySearch array 3

51 echo -e
"$?/t$times"

52 binarySearch array 101

53 echo -e
"$?/t$times"

54

55 exit 0



write by 九天雁翎(JTianLing) -- blog.csdn.net/vagrxie