Question

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.

Solution

/* 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 l = 1, r = n;
        while(r - l > 1) {
            int mid = l + (h - l) / 2; // be careful of overflow
            int g = guess(mid);
            if (g == 0) return mid;
            else if(g == 1) l = mid;
            else r = mid;
        }
        return guess(l) == 0 ? l : r;
    }
}