思路：二分查找，注意溢出問題

/* 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 low = 1 ,high = n;		while (true) {			int mid = low + (high - low) / 2;			if (guess(mid) == 0)				return mid;			else if (guess(mid) == -1)				high = mid - 1;			else    			low = mid + 1;		}    }}
Runtime：1ms