python实现二分法（迭代+循环）

迭代实现：

def dichotomy_iter(L,find_num,left,right):
	# 取中间值的索引
	middle=(left+right)//2
	if L[middle]==find_num:
		return middle
	if left>right:
		return -1
	if L[middle]>find_num:
		return dichotomy_iter(L,find_num,left,middle)
	if L[middle]<find_num:
		return dichotomy_iter(L,find_num,middle,right)

调用：

L=[1,2,3,4,5,8,16,20,30,40,60,70,1112,1231]
print(dichotomy_iter(L,40,0,len(L)))

循环实现：

def dichotomy_loop(list, key):
	left = 0     # 左边界
	right = len(list) - 1   # 右边界
	while left <= right:
		mid = (left + right) // 2  # 取得中间索引
		if key > list[mid]:
			left = mid + 1
		elif key < list[mid]:
			right = mid - 1
		else:
			return mid
	else:
		return -1

调用：

L=[1,2,3,4,5,8,16,20,30,40,60,70,1112,1231]
print(dichotomy_loop(L,40))