Guess Number Higher or Lower

Problem: Guess Number Higher or Lower

Code in Python:

# The guess API is already defined for you.
# @param num, your guess
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num):

class Solution(object):
    def guessNumber(self, n):
        """
        :type n: int
        :rtype: int
        """
        l, r = 0, n
        while l < r:
            c = (l + r + 1) / 2
            if guess(c) == 0: return c
            elif guess(c) == -1: r = c-1
            else: l = c+1
        return l