先來看個用Python實現的二分查詢演算法例項

#!/usr/bin/env 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)

執行:

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

注:

1.'__'：由於python的類成員都是公有、公開的被存取public，缺少像正統面嚮物件語言的私有private屬性。

於是就用__來將就一下，模擬私有屬性。這些__屬性往往是內部使用，通常情況下不用改寫。也不用讀取。

加上2個下劃線的目的，一是不和普通公有屬性重名衝突，二是不讓物件的使用者(非開發者)隨意使用。

2.__name__ == "__main__"表示程式指令碼是直接被執行的.

如果不等於表示指令碼是被其他程式用import引入的.則其__name__屬性被設為模組名

Python採用二分查詢找出數字的下標

要考慮有重複數字的情況

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:" 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))

  

</target:>

二分演算法的定義不在多說了

'fileName--BinarySearch.py'最後在分享一個

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

原文至：https://www.py.cn/jishu/jichu/10384.html