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!

Example:

n = 10, I pick 6.Return 6.

参考模板：模板：Binary Search - 二分搜索。这道题可以用lowerbound的模板也可以用upperbound的模板，不过推荐用lowerbound的模板，不然要额外判断一次upperbound。因为这里的数是1-n，如果选择0-n+1，当n等于Integer.MAX_VALUE时int mid = lb + (ub - lb) / 2;会越界，那么就只能选0-n，所以用lowerbound比较好，0+1正好是1-n的开头。代码如下：

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