python（四）二分查找法

# coding:utf-8

import random
import time

def sort(alist, first, last):
    if first >= last:
        return
    mid_value = alist[first]
    low = first
    high = last
    while low < high:
        while low < high and alist[high] >= mid_value:
            high -= 1
        alist[low] = alist[high]
        while low <high and alist[low] < mid_value:
            low += 1
        alist[high] = alist[low]
    alist[low] = mid_value
    sort(alist, first, low-1)
    sort(alist, low+1, last)

def binary_search(alist, item):
    """递归"""
    n = len(alist)
    if n > 0:
        mid = n//2
        if alist[mid] == item:
            return True
        elif item < alist[mid]:
            return binary_search(alist[:mid], item)
        else:
            return binary_search(alist[mid+1:], item)
    return False



def binary_search_2(alist, item):
    """非递归"""
    n = len(alist)
    first = 0
    last = n-1
    while first <= last:
        mid = (first + last)//2
        if alist[mid] == item:
            return True
        elif item < alist[mid]:
            last = mid - 1
        else:
            first = mid + 1
    return False

if __name__ == "__main__":
    seq = list(range(1, 10000))
    li = random.sample(seq, 1000)
    sort(li, 0, len(li) - 1)
    print(li)
    start = time.clock()
    # print(binary_search(li, 104))
    print(binary_search_2(li, 104))
    end = time.clock()
    print("time: %f " % (end - start))