太忙了，这次写不了题解啦

A

·模拟

#include <bits/stdc++.h>

using namespace std;

int n, m, k;

int main()
{
    int T;

    cin >> T;
    while(T --)
    {

        cin >> n >> m;

        vector<int> a(n);
        for(int i = 0; i < n; i ++) cin >> a[i];
        sort(a.begin(), a.end());
        reverse(a.begin(), a.end());

        int ff = a[0], ss = a[1];
        int r = (m / (ff + ss)) * 2;
        m %= (ff + ss);

        if(!m) cout << r << endl;
        else if(m > ff) cout << r + 2 << endl;
        else cout << r + 1 << endl;
    }

    return 0;
}

B

·找规律

#include <bits/stdc++.h>

using namespace std;

int n, m;

int main()
{
    int T;
    cin >> T;
    while(T --)
    {
        cin >> n >> m;

        vector<int> a(n), b(n);
        for(int i = 0; i < n; i ++) cin >> a[i], b[i] = a[i];
        sort(b.begin(), b.end());

        bool suc = true;
        for(int i = n - m; i <= m - 1; i ++) if(b[i] != a[i]) suc = false;

        if(suc) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
}

C

·数学（？

#include<bits/stdc++.h>

using namespace std;

const int N = 1e5 + 10;
int t, n, k, x, y, a[N], cnt;
bool st[N];
vector<int> h[N];

int dfs(int i, int s)
{
    int u = a[i];
    st[i] = true;

    for(auto x : h[i]) if(!st[x]) u ^= dfs(x, s);

    if(u == s)
    {
        cnt ++;
        return 0;
    }

    return u;
}

int main()
{
    cin >> t;
    while(t --)
    {
        cin >> n >> k;

        int s = 0;
        for(int i = 1; i <= n; i ++) cin >> a[i], s ^= a[i], h[i].clear();

        for(int i = 1; i < n; i ++)
        {
            cin >> x >> y;
            h[x].push_back(y);
            h[y].push_back(x);
        }

        if(!s)
        {
            cout << "YES\n";
            continue;
        }

        cnt = 0;
        memset(st, 0, sizeof st);
        dfs(1, s);

        if(cnt >= 3 && k >= 3) cout << "YES\n";
        else cout << "NO\n";
    }
}

D

·dfs

#include<bits/stdc++.h>

using namespace std;

const int N = 1117;
pair<int, int> sides[N];
vector<int> h[N];
bool st[N];

int n, x, y, t, cnt;

void dfs(int a, int b)
{
    sides[++cnt] = {a, b};
    for(auto u : h[b]) if(u != a) dfs(b, u);
}

int main()
{
    cin >> n;
    for(int i = 1; i < n; i ++) cin >> x >> y, h[x].push_back(y), h[y].push_back(x);

    for(auto i : h[1]) dfs(1, i);

    cout << "? " << n;
    for(int i = 1; i <= n; i ++) cout << ' ' << i;
    cout << endl;
    cin >> t;

    int l = 1, r = n - 1, m;
    while(l < r)
    {
        m = l + r >> 1;
        set<int> s;
        for(int i = l; i <= m; i ++) s.insert(sides[i].first), s.insert(sides[i].second);
        cout << "? " << s.size() << ' ';
        for(auto i : s) cout << i << ' ';
        cout << endl;
        int u;
        cin >> u;
        if(t == u) r = m;
        else l = m + 1;
    }

    cout << "! " << sides[l].first << ' ' << sides[l].second << endl;
}