Guess Number Higher or Lower

题目
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):

答案

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