用Python实现的二分查找算法

#!/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)

运行:

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

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:" 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:>

二分算法的定义不在多说了

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!')