Description： 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

題意：模擬一個猜數字的遊戲，給定一個範圍[1,n]，猜測在這個範圍內的一個數字，每一次的猜測都會給出你所猜的是大了，小了，還是正確找到那個數字，返回所要猜測的那個數字；

解法：根據題意相當於讓我們實現二分查詢，每次猜測一個數字後判斷是否是要找的那個數，或者是偏大了，或者是偏小了，總之，根據guess函式的返回值，我們來實現二分查詢；

Java

/* 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) {
        long low = 1;
        long high = n;
        while (low <= high) {
            long mid = (low + high) / 2;
            int gus = guess((int)mid);
            if (gus == 0) return (int)mid;
            else if (gus == -1) high = mid - 1;
            else low = mid + 1;
        }
        return -1;
    }
}