374. Guess Number Higher or Lower*

374. Guess Number Higher or Lower*

https://leetcode.com/problems/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 :

Input: n = 10, pick = 6
Output: 6

C++ 实现 1

内部 pick 了一个 number, 提供的 API 用来判断这个 number 是否比当前我们猜测的元素 mid 相等. 如果大, 则返回 1, 相等则返回 0, 小的话则返回 -1.

/** 
 * Forward declaration of guess API.
 * @param  num   your guess
 * @return 	     -1 if num is lower than the guess number
 *			      1 if num is higher than the guess number
 *               otherwise return 0
 * int guess(int num);
 */

class Solution {
public:
    int guessNumber(int n) {
        int l = 1, r = n;
        while (l <= r) {
            int mid = l + (r - l) / 2;
            if (guess(mid) == 0) return mid;
            else if (guess(mid) == 1) l = mid + 1;
            else r = mid - 1;
        }
        return -1;
    }
};