374. Guess Number Higher or Lower | LeetCode

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.

一开始理解错题意了答错了好几次，正如讨论区一个帖子所说：

the key point is to read the problem carefully

注意，判断大小时是基于 pick number 判断。因为是反复比较大小，所以可以联想到二分法。但是要注意到常规二分法如：mid = (low + high) / 2，有可能在计算最大数和最小数相加时出现溢出，所以 mid 的求法要改变一下。代码如下：

public class Solution extends GuessGame {    public int guessNumber(int n) {        int low = 1;        int high = n;        int mid;        while(high >= low) {            mid = low + (high - low) / 2; //注意 mid 求法，其实就是 low / 2 + high / 2            int g = guess(mid);            if(g == 0) return mid;            if(g == 1) low = mid + 1;            else high = mid;                }        return n;    }}