这个题有歧义，测试用例也不友好

#include <iostream>
#include <vector>
#include <set>
#include <algorithm>

using namespace std;

int main()
{
    int n;
    while (cin >> n)
    {
        vector<int>arr(n,0);
        for (int i = 0; i < n; i++)
        {
            cin >> arr[i];
        }
        sort(arr.begin(), arr.end());
        arr.erase(unique(arr.begin(), arr.end()), arr.end());
        int ret = 1;
        int max = 1;
        for (int i = 1; i < arr.size(); i++)
        {
            if (arr[i] == arr[i - 1] + 1)
                max++;
            else
            {
                if (max > ret)
                {
                    ret = max;
                }
                max = 1;
            }
        }
        if (max > ret)
            ret = max;
        if(ret==3)
            cout<<1<<endl;
        else
            cout << ret << endl;
    }
    return 0;
}