4A - Horse

打表找规律

#include <iostream>
#include <queue>
using namespace std;
bool vis[][];
int dx[]{, , , , -, -, -, -};
int dy[]{, -, , -, , -, -, };
struct point
{
    int x;
    int y;
    int deep;
};
queue<point> q;

int bfs(int n)
{
    while (!q.empty())
        q.pop();
    memset(vis, false, sizeof(vis));
    point head;
    head.x = head.y = ;
    head.deep = ;
    q.push(head);
    vis[head.x][head.y] = true;

    int sum = ;
    while (!q.empty()) {
        head = q.front();
        q.pop();
        point np;
        for (int i = ; i < ; i++) {
            np.x = head.x + dx[i];
            np.y = head.y + dy[i];
            np.deep = head.deep + ;
            if (np.x >=  && np.x <=  && np.y >=  && np.y <=  && !vis[np.x][np.y] && np.deep <= n) {
                vis[np.x][np.y] = true;
                q.push(np);
                sum++;
            }
        }
    }
    return sum;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie();

    int arr[];
    for (int i = ; i <= ; i++) {
        arr[i] = bfs(i);
        cout << arr[i] << ' ';
    }
    cout << endl;
    int b[];
    int k = ;
    for (int i = ; i <= ; i++) {
        b[k] = arr[i] - arr[i - ];
        cout << b[k++] << ' ';
    }
    cout << endl;
    for (int i = ; i < k; i++)
        cout << b[i] - b[i - ] << ' ';
    cout << endl;
    return ;
}

打表发现第五项205开始，后一项减前一项的差值(第二排)，再与之后的差值做差值，值都是28.

最终结果:

#include <iostream>
using namespace std;
typedef unsigned long long ull;
int arr[] {, , , , };

int main()
{
    ios::sync_with_stdio(false);
    cin.tie();
    int t;
    cin >> t;
    while (t--) {
        ull n;
        cin >> n;
        if (n < )
            cout << arr[n] << endl;
        else {
            ull diff = n - ;
            cout <<  + diff *  + (diff - ) * diff *  << endl;
        }
    }
    return ;
}