Binary Search 二分查找

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

易错点：

h = mid     当A=[0], val = -1

l  = mid     当A=[0], val = 1

l <= h        当len(A) = 1: