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):

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-1 : My number is lower
 1 : My number is higher
 0 : Congrats! You got it!

Example:

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n = 10, I pick 6.
Return 6.

思路

利用二分法进行搜索。

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# 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
        """
        high = n
        low = 0
        while (low <= high):
            mid = low + (high - low) / 2
            if (guess(mid) == -1):
                high = mid - 1
            elif (guess(mid) == 1):
                low = mid + 1
            else:
                break
        return (high + low)/2

参考资料：

Jon Bentley：90%程序员无法正确实现二分查找算法
https://www.cnblogs.com/ider/archive/2012/04/01/binary_search.html
http://hedengcheng.com/?p=595
https://research.googleblog.com/2006/06/extra-extra-read-all-about-it-nearly.html