Guess Number Higher or Lower

题目地址：https://leetcode.com/problems/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!

Example:

n = 10, I pick 6.
Return 6.

很简单，还是二分查找法，反正1到n是有序的：

/**
 * 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 GuessNumberHigherOrLower {
    /*public static int guess(int num) {
        if (num > 6)
            return 1;
        else if (num == 6)
            return 0;
        else
            return -1;
    }*/

    public static int guessNumber(int n) {
        return guessNumberRecur(1, n);
    }

    public static int guessNumberRecur(int low, int high) {
        System.out.println(low + " " + high);
        if (low == high)
            return low;
        int mid = low + (high - low) / 2;
        if (guess(mid) == 0)
            return mid;
        else if (guess(mid) == -1)
            return guessNumberRecur(low, mid);
        else
            return guessNumberRecur(mid + 1, high);
    }

    public static void main(String[] args) {
        System.out.println(guessNumber(100));
    }
}

时间复杂度为O(logn)。