二分查找（算法）（原创） 

 #给定一个有序数组和目标值，查找目标值出现在给定数组中的区间范围，复杂度要求为O（log n），若无目标区间值则区间为[-1,-1] 

 1 # -*- coding: utf-8 -*-
 2 """
 3 Created on Tue Oct 10 09:04:53 2017
 4 
 5 @author: nvidia
 6 """
 7 
 8 #!/usr/bin/python
 9 #coding=utf-8
10 #自定义函数，实现二分查找，并返回查找结果
11 def binary_search(find, foo) :
12   low = 0
13   high = len(foo)
14   while low <= high :
15   mid = (low + high) / 2
16   if foo[mid] == find :
17   return mid
18   #左半边
19   elif foo[mid] > find :
20   high = mid -1
21   #右半边
22   else :
23   low = mid + 1
24   #未找到返回-1
25   return -1
26 foo = [1,3,3,4,4,8,11,18]
27 #进行二分查找算法前必须保证要查找的序列时有序的，这里是升序列表
28 foo.sort()
29 print "原有序列表为:",foo
30 try :
31   find = int(raw_input("请输入要查找的数："))
32 except :
33   print "请输入正整数！"
34   exit()
35 result = binary_search(find, foo)
36 if result != -1 :
37   if result == 0:
38   print "[%d,%d]" %(foo[0],foo[1])
39   #考虑到查找值序号为0时，前置数值没有的情况
40   else :
41   print "[%d,%d]" %(foo[result-1],foo[result])
42   #正常查找值情况
43 
44 else :
45   print "[-1,-1]"
46   #无查找值情况
47 
48 """
49 the down words are the result.
50 system:ubuntu Jetson TX2
51 
52 Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
53 Type "copyright", "credits" or "license" for more information.
54 
55 IPython 2.4.1 -- An enhanced Interactive Python.
56 ? -> Introduction and overview of IPython's features.
57 %quickref -> Quick reference.
58 help -> Python's own help system.
59 object? -> Details about 'object', use 'object??' for extra details.
60 %guiref -> A brief reference about the graphical user interface.
61 
62 In [1]: runfile('/home/nvidia/Documents/work/20171010.py', wdir='/home/nvidia/Documents/work')
63 原有序列表为: [1, 3, 3, 4, 4, 8, 11, 18]
64 
65 请输入要查找的数：4
66 [4,4]
67 
68 In [2]: runfile('/home/nvidia/Documents/work/20171010.py', wdir='/home/nvidia/Documents/work')
69 原有序列表为: [1, 3, 3, 4, 4, 8, 11, 18]
70 
71 请输入要查找的数：8
72 [4,8]
73 
74 In [3]: runfile('/home/nvidia/Documents/work/20171010.py', wdir='/home/nvidia/Documents/work')
75 原有序列表为: [1, 3, 3, 4, 4, 8, 11, 18]
76 
77 请输入要查找的数：10
78 [-1,-1]
79 
80 """





 

 

posted on 2017-10-10 19:30  周健康  阅读(339)  评论(0)  编辑  收藏  举报

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