[Swift]LeetCode374. 猜数字大小 | Guess Number Higher or Lower

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➤微信公众号：山青咏芝（shanqingyongzhi）
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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.

---

我们正在玩一个猜数字游戏。 游戏规则如下：
我从 1 到 n 选择一个数字。 你需要猜我选择了哪个数字。
每次你猜错了，我会告诉你这个数字是大了还是小了。
你调用一个预先定义好的接口 guess(int num)，它会返回 3 个可能的结果（-1，1 或 0）：

-1 : 我的数字比较小
 1 : 我的数字比较大
 0 : 恭喜！你猜对了！

示例 :

输入: n = 10, pick = 6
输出: 6

---

8ms

class Solution {
    func guessNumber(_ n: Int, _ pick: Int) -> Int {
        if pick == n {return n}
        var left:Int = 1
        var right:Int = n
        while(left < right)
        {
            var mid = left + (right - left)/2
            if pick == mid
            {
                return mid
            }
            else if pick < mid
            {
               right = mid
            }
            else
            {
                left = mid
            }
        }
        return -1
    }
}

---

C++版本：

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