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