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:
n = 10, I pick 6.

Return 6.

这个是二分法找数

/* 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 result=-1;
        int low=1;
        int high=n;
        while (result!=0) {
            n=low+(high-low)/2;
            result = guess(n);
            if (result==0) 
                return n;
            if (result>0) 
                low = n+1;
            if (result<0) 
                high = n-1;
        }
        return 0;
    }
}