Guess Number Higher or Lower

LeetCode Q 374 - Guess Number Higher or Lower

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!

Solution

Code:

/* 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 int guessNumber(int n) {
	int left = 1, right = n;
	while (left <= right) {
		int mid = left + (right - left) / 2;
		if (guess(mid) == 0) return mid;
		else if (guess(mid) == -1) right = mid - 1;
		else left = mid + 1;
	}
	return -1;
}