1.Cthulhu(https://codeforces.com/problemset/problem/103/B)

#include <bits/stdc++.h>
#define iter(i,x,y) for (int i = x; i <= y; i ++)
#define defN(x, y) const int y = x
#define endl(x) for (int i = 0; i < x; i ++ ) cout << endl
using namespace std;
using int64 = long long;

defN(1100, N);
int n, m;
int e[N], ne[N], h[N], idx;
bool vis[N];

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}

void bfs(int x) 
{
    int q[N], hh = 0, tt = -1;
    q[++ tt] = x;
    while (hh <= tt) {
        int t = q[hh ++];
        vis[t] = true;
        for (int i = h[t]; i != -1; i = ne[i]) {
            if (vis[e[i]]) continue;
            else q[++ tt] = e[i];
        }
    }
}

bool judge()
{
    iter(i, 1, n) if (!vis[i]) return false;
    return true;
}

void solve()
{
    cin >> n >> m;
    memset(h, -1, sizeof h);
    iter(i, 1, m) {
        int x, y;
        cin >> x >> y;
        add(x, y);
        add(y, x);
    }

    bfs(1);

    if (n != m || (!judge())) cout << "NO" << endl;
    else cout << "FHTAGN!" << endl;

    return;
}

int main()
{
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int T = 1;//注意题给条件，这个T可能要初始化为1
    while (T -- ) solve();

    return 0;
}

2.Jumping on Walls(https://codeforces.com/problemset/problem/198/B)

#include <bits/stdc++.h>
#define iter(i,x,y) for (int i = x; i <= y; i ++)
#define defN(x, y) const int y = x
#define endl(x) for (int i = 0; i < x; i ++ ) cout << endl
using namespace std;
using int64 = long long;
typedef pair<int, int> PII;
typedef tuple<int,int,int> TRI;
typedef unsigned long long ULL;

struct pos{
    int h, id, t;
};

void solve()
{
    int n, k; cin >> n >> k;
    vector<vector<int>> a(2);
    a[0].push_back(0); a[1].push_back(0);   

    iter(i, 0, 1) iter(j, 1, n) {
        char c; cin >> c;
        if (c == 'X') a[i].push_back(1);
        else if (c == '-') a[i].push_back(0);
    }

    //iter(i, 0, 1) iter(j, 0, n - 1) cout << a[i][j] << " \n"[j == n - 1];

    queue<pos> q;
    q.push((pos) {1, 0, 0}), a[0][1] = 1;
    while (q.size()) {
        pos t = q.front(), nw; q.pop();
        nw = t; nw.h --; nw.t ++;
        if (nw.h > 0 && !a[nw.id][nw.h] && nw.t < nw.h)
            a[nw.id][nw.h] = 1, q.push(nw);
        nw = t; nw.h ++; nw.t ++;
        if(nw.h > n) {cout << "YES" << endl; return;}
        if (nw.h > 0 && !a[nw.id][nw.h] && nw.t < nw.h)
            a[nw.id][nw.h] = 1, q.push(nw);
        nw = t; nw.h += k; nw.id = !nw.id; nw.t ++;
        if(nw.h > n) {cout << "YES" << endl; return;}
        if (nw.h > 0 && !a[nw.id][nw.h] && nw.t < nw.h)
            a[nw.id][nw.h] = 1, q.push(nw);
    }
    cout << "NO" << endl;
    return;
}

int main()
{
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int T = 1;//注意题给条件，这个T可能要初始化为1
    while (T -- ) solve();

    return 0;
}