problem_374.java

/**
 * 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 (the number I picked stays the same throughout the game).
Every time you guess wrong, I will tell you whether the number I picked is higher or lower than your guess.
You call a pre-defined API int guess(int num), which returns three possible results:
    -1: Your guess is higher than the number I picked (i.e. num > pick).
    1: Your guess is lower than the number I picked (i.e. num < pick).
    0: your guess is equal to the number I picked (i.e. num == pick).
Return the number that I picked.
*/


/** 
 * 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 l = 1, h = n, mid;
        while(l <= h){
            mid = l + (h - l) / 2;
            int pick = guess(mid);
            if(pick == 0) return mid;
            else if(pick == 1) l = mid+1;
            else h = mid-1;
        }
        return -1;
    }
}