Binary Search 二分查找

def binarySearch(A,val):
	if A == None or len(A) == 0:
		return None	
	l = 0
	h = len(A) - 1
	
	while l <= h:
		mid = l + (h-l) / 2
		if A[mid] > val:
			h = mid - 1
		elif A[mid] < val:
			l = mid + 1
		else:
			return mid
	return None

易错点：

h = mid     当A=[0], val = -1

l  = mid     当A=[0], val = 1

l <= h        当len(A) = 1: