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：Binary Search

Time Complexity: O(logN) Space Complexity: O(1)

Solution Code：

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int start = 1, end = n;
        while(start < end) {
            int mid = start + (end - start) / 2;
            if(guess(mid) == 0) {
                return mid;
            } else if(guess(mid) == 1) {
                start = mid + 1;
            } else {
                end = mid;
            }
        }
        return start;
    }
}