LeetCode/java/guess-number-higher-or-lower.java

/**
 * 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);
 */
class Solution extends GuessGame {
  private enum Response {
    Smaller(-1),
    Exact(0),
    Bigger(1);

    public final int value;

    private Response(int value) {
      this.value = value;
    }
  }

  public int guessNumber(int n) {
    int lower = 1;
    int upper = n;

    while (true) {
      var mid = lower + (upper - lower) / 2;

      int response = guess(mid);
      if (response == Response.Exact.value) {
        return mid;
      } else if (response == Response.Smaller.value) {
        upper = mid - 1;
      } else if (response == Response.Bigger.value) {
        lower = mid + 1;
      } else {
        // invalid response
        return -1;
      }
    }
  }
}