Python二分法搜索算法实例分析

#!/usr/bin/env python
#encoding: utf-8
def half_search(search_arr, search_str):
  lb = 0
  ub = len(search_arr) - 1
  for i in range(ub/2 + 1):
    if lb > ub:
      return -1
    mid = (ub + lb)/2
    if search_arr[mid] == search_str:
      return mid
    elif search_arr[mid] > search_str:
      ub = mid - 1
    else:
      lb = mid + 1
if __name__=='__main__':
  arr = [10,20,30,40,50,60,70]
  print half_search(arr, 1)
  print half_search(arr, 11)
  print half_search(arr, 22)
  print half_search(arr, 33)
  print half_search(arr, 40)
  print half_search(arr, 55)
  print half_search(arr, 66)
  print half_search(arr, 70)
  print half_search(arr, 8)

-1 
-1 
-1 
-1 
3 
-1 
-1 
6 
-1