0374. Guess Number Higher or Lower #

题目 #

猜数字游戏 规则如下：
- 从 1 到 n 随机选择一个数字。猜出被选择的这个数字。
- guess 函数会返回所猜数字与所选数字的大小关系。
  - -1：所选数字小于所猜数字
  - 1：所选数字大于所猜数字
  - 0：所选数字等于所猜数字
返回所选数字。

思路 #

二分 #

代码 #

二分 #

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

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int left = 1, right = n;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (guess(mid) == 0) return mid;
            else if (guess(mid) == -1) right = mid - 1;
            else left = mid + 1;
        }
        return -1;
    }
}