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 :
Input: n = 10, pick = 6
Output: 6

ideas(二分查找)

/* 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 s = 0, r = n, mid = 0;
        
        if (guess(n) == 0) return n;
        
        while (s < r) {
            mid = s + (r - s) / 2;
            if (guess(mid) == 0) {
                return mid;
            } else if (guess(mid) > 0) {
                s = mid + 1;
            } else {
                r = mid - 1;
            }
        }