LeetCode 374. Guess Number Higher or Lower

'''
We are playing the Guess Game. The game is as follows:

I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I'll tell you whether the number is higher or lower.

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):

-1 : My number is lower
 1 : My number is higher
 0 : Congrats! You got it!
'''
# 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
        """
        i = 1
        while n > i+1:
            j = (i+n)//2
            if guess(j) == -1:
                n = j
            elif guess(j) == 1:
                i = j
            else:
                return j
        if guess(i) == 0:
            return i
        else:
            return n