Python [Leetcode 374]Guess Number Higher or Lower

题目描述：

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!

Example:

n = 10, I pick 6.

Return 6.

解题思路：

二分查找法的变体

代码如下：

# 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
        """
        left, right = 1, n
        while(left <= right):
        	mid = (left + right) / 2
        	res = guess(mid)
        	if res == 0:
        		return mid
        	elif res == -1:
        		right = mid -1
        	elif res == 1:
        		left = mid + 1

        return -1