[leetcode] 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.

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这道题和刚刚那道first bad version几乎一模一样，同样考虑到相加溢出问题而选择mid = left + (right - left) / 2;

刚开始没理解 My number is lower 中的my指的是给出值还是猜的值更小出现错误。

我的代码如下：

// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
    int guessNumber(int n) {
        int left = 1, right = n;
        int mid;
        while (left < right) {
            mid = left + (right - left) / 2;
            int result = guess(mid);
            if (result == 0) return mid;
            if (result == 1) left = mid + 1;
            else right = mid - 1;
        }
        return left;
    }
};