Python二分查找详解

先来看个实例

#!/usr/bin/env python/' target='_blank'>python import sys   def search2(a,m):   low = 0    high = len(a) - 1    while(low <= high):     mid = (low + high)/2     midval = a[mid]        if midval < m:       low = mid + 1      elif midval > m:       high = mid - 1      else:       print mid        return mid    print -1   return -1  if __name__ == "__main__":   a = [int(i) for i in list(sys.argv[1])]   m = int(sys.argv[2])   search2(a,m) 

运行:

administrator@ubuntu:~/Python$ python test_search2.py 123456789 4

3

注:

1.'__'：由于python的类成员都是公有、公开的被存取public，缺少像正统面向对象语言的私有private属性。
于是就用__来将就一下，模拟私有属性。这些__属性往往是内部使用，通常情况下不用改写。也不用读取。
加上2个下划线的目的，一是不和普通公有属性重名冲突，二是不让对象的使用者(非开发者)随意使用。
2.__name__ == "__main__"表示程序脚本是直接被执行的.
如果不等于表示脚本是被其他程序用import引入的.则其__name__属性被设为模块名

Python采用二分查找找出数字的下标

要考虑有重复数字的情况

class Solution(object):  def searchRange(self, nums, target):    """    :type nums: List[int]    :type target: int    :rtype: List[int]    """    def binary_search(start,end,value):      while end>=start:        mid = (start+end)//2        print(mid)        if nums[mid]>target:          end = mid-1        elif nums[mid]<target:          start = mid+1        else:           if value==-1:            if mid-1>=start and nums[mid+value] == target:              end = mid+value            else:              return mid          else:            if mid+1<=end and nums[mid+value] == target:              start = mid+value            else:              return mid       return -1    a=binary_search(0,len(nums)-1,-1)    b=binary_search(0,len(nums)-1,1)    return [a,b]a = Solution()l = [2,2]print(a.searchRange(l,2))

二分算法的定义不在多说了，百度一下就知道（支持国产大笑）

import sys source = [1,2,3,4,5,6,7,8,9,10] #must be in order des = int(sys.argv[1]) low = 0 high = len(source) - 1 targetIndex = -1 print "des=",des while low <= high:   middle = (low + high)/2   if des == source[middle]:     targetIndex = middle     break   elif des < source[middle]:     high = middle -1     print "middle element[index=",middle,",value=",source[middle],"] is bigger than des, continue search from[",low,"to",high,"]"   else:     low = middle + 1     print "middle element[index=",middle,",value=",source[middle],"] is smaller than des, continue search from[",low,"to",high,"]" print "search complete, target element's index in source list is ",targetIndex 

最后在分享一个

'fileName--BinarySearch.py'  src = []  def BinarySearch(low, high, target, *src):   '二分查找'   while low <= high:     mid = (low + high) // 2     midVal = src[mid]     if target < midVal:       high = mid - 1     elif target > midVal:       low = mid + 1     else:       return mid     BinarySearch(low, high, target, *src)  print('Please input 10 number:') for number in range(10):   src.append(int(input('Num %d:' % number)))  sortList = tuple(src)  key = int(input('Please input key:')) location = BinarySearch(0, len(src) - 1, key, *sortList)  if location != None:   print('Find target at %d' % (location + 1)) else:   print('No target!')