# 374.Guess Number Higher or Lower

**374.Guess Number Higher or Lower**

难度:Easy

> 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
```

方法：二分法。 需要注意一些特殊情况。当mid==start时，有可能无限循环。比如(1+2)/2=1,这时将mid++即可。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 start=1;
        int ed=n;
        int t=1;
        int mid;
        while(start<ed)
        {
            mid=start+(ed-start)/2;
            
          //  cout <<start<<" "<<ed<<" "<< mid<<" "<<t<<endl;
            t=guess(mid);
            if(t==0) return mid;
            if(mid==start) mid++;
            if(t==-1)
                ed=mid;              
            else if(t== 1)
                start=mid;
          
           
        }
       // cout<<guess(7)<<endl;
        return start;
    }
};
```


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