374. Guess Number Higher or Lower

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
题目很明显的二分查找,有序数列，找固定数字

/* The guess API is defined in the parent class GuessGame.
   @param num, your guess
   @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
      int guess(int num); */

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int low=1,high=n,mid;
        while(low<=high){
            mid=low+(high-low)/2;
            if(guess(mid)==0)   return mid;
            else if(guess(mid)==1) low=mid+1;
            else    high=mid-1;
        }
        //任意返回值都能ac，不加的话leetcode编译的时候会报错
        return 1;
    }
}