[LeetCode] 374. Guess Number Higher or Lower_Easy tag: Binary Search

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.


思路也是典型的Binary Search, 只是需要注意的是guess(num) 每次对应的是猜的数高了, 还是答案高了即可.

Code

# 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):
        l, r = 1, n
        while l + 1 < r:
            mid = l + (r-l)//2
            num = guess(mid)
            if num == 1:
                l = mid
            elif num == -1:
                r = mid
            else:
                return mid
        return l if guess(l) == 0 else r