Submission #922128

#	Time	Username	Problem	Language	Result	Execution time	Memory
922128		406	Newspapers (CEOI21_newspapers)	C++17	100 / 100	1 ms	860 KiB

newspapers

    #include "bits/stdc++.h"
    #define int long long
    #define FOR(i, a, b) for (int i = (a); i < (b); i++)
    using namespace std;
    const long long INF = 1ll << 60;
    const int N = 1000 + 5;
    int h[N], pr[N];
    vector<int> adj[N], V[N], order;
    bitset<N> leaf;
     
    void dfs(int v, int p) {
    	for (auto u: adj[v]) if (u != p) {
    		h[u] = h[v] + 1;
    		pr[u] = v;
    		dfs(u, v);
    	}
    }
     
    signed main() {
    	ios::sync_with_stdio(0), cin.tie(0);
    	int n, m;
    	cin >> n >> m;
    	if (m >= n) {
    		cout << "NO\n";
    		return 0;
    	}
    	if (n <= 2) {
    		cout << "YES\n";
    		cout << n << '\n';
    		FOR(i, 0, n) cout << 1 << ' ';
    		return 0;
    	}
    	FOR(i, 1, n) {
    		int u, v; cin >> u >> v;	
    		u--, v--;
    		adj[u].push_back(v);
    		adj[v].push_back(u);
    	}
    	FOR(i, 0, n) leaf[i] = adj[i].size() == 1;
    	FOR(i, 0, n) if (!leaf[i]) {
    		vector<int> t;
    		for (auto u: adj[i]) if (!leaf[u]) t.push_back(u);
    		adj[i] = t;
    	}
    	//is caterpillar?
    	FOR(i, 0, n) {
    		int ch = 0;
    		for (auto u: adj[i]) ch += adj[u].size() > 1;
    		if (ch >= 3) {
    			cout << "NO\n";
    			return 0;
    		}
    	}
    	int U, V;
    	FOR(i, 0, n) if (!leaf[i]) {
    		memset(h, -0x3f, sizeof h);
    		h[i] = 0;
    		dfs(i, i);
    		U = max_element(h, h + n) - h;
    		memset(h, -0x3f, sizeof h);
    		h[U] = 0;
    		dfs(U, U);
    		V = max_element(h, h + n) - h;
    		break;
    	}
    	//U, V is diam. 
    	for (int t = V; t != U; t = pr[t]) {
    		order.push_back(t);
    		for (auto u: adj[t]) if (!leaf[u] && adj[u].size() == 1 && u != V && u != U) 
    			order.push_back(u), order.push_back(t);
    	}
    	order.push_back(U);
     
    	cout << "YES\n";
    	cout << order.size() * 2 << '\n';
    	for (auto u: order) cout << u + 1 << ' ';
    	reverse(order.begin(), order.end());
    	for (auto u: order) cout << u + 1 << ' ';
    	cout << '\n';
    	return 0;
    }
    // this fills you with ....

Compilation message (stderr)

newspapers.cpp: In function 'int main()':
newspapers.cpp:69:63: warning: 'V' may be used uninitialized in this function [-Wmaybe-uninitialized]
   69 |       for (auto u: adj[t]) if (!leaf[u] && adj[u].size() == 1 && u != V && u != U)
      |                                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~

• Subtask 1: 12 / 12
• Subtask 2: 8 / 8
• Subtask 3: 80 / 80