猜数字大小（简单）

/** 
 * 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);
 */

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int l=1;
        int r=n;
        while(l<=r){
            int c=l+(r-l)/2;
            int num=guess(c);
            if(num==0) return c;
            else if(num==-1) r=c-1;
            else l=c+1;
        }
        return -1;
    }
}