Submission #161625

#	Time	Username	Problem	Language	Result	Execution time	Memory
161625		amoo_safar	Mousetrap (CEOI17_mousetrap)	C++14	100 / 100	1524 ms	238072 KiB

mousetrap

#include <bits/stdc++.h>
 
#define pb push_back
#define F first
#define S second
 
using namespace std;
 
typedef long long ll;
typedef string str;
 
const ll Mod = 1e9 + 7;
const int Maxn = 1e6 + 100;

vector<ll> G[Maxn];
ll dp[Maxn], son[Maxn], m1[Maxn], m2[Maxn];
ll t, m;
vector<ll> V;
vector<ll> S[Maxn];
bool DFS(ll u, ll p){
	bool res = (u == m), r2;
	ll cnt = 0;
	ll mx = 0;
	ll mx2 = 0;
	
	for(auto adj : G[u]){
		if(adj == p) continue;
		r2 =DFS(adj, u);
		res |= r2;
		if(!r2){
			S[u].pb(adj);
			cnt ++;
			if(dp[adj] > mx){
				mx2 = mx;
				mx = dp[adj];
			} else mx2 = max(mx2, dp[adj]);
		}
	}
	dp[u] = cnt + mx2;
	m2[u] = mx2;
	m1[u] = mx;
	son[u] = cnt;
	if(res){
		V.pb(u);
	}
	return res;
}
ll dp2[Maxn];
vector< pair<ll, ll> > A;
ll C[Maxn];

bool CMP(ll i, ll j){
	return dp[i] > dp[j];
}
ll ps[Maxn];

bool check(ll x){
	ll M = V.size();
	ll c = 0;
	for(int i = 0; i < M - 1; i++){
		ll SS = S[V[i]].size();
		for(int j = 0; j < SS; j++){
			if(c + dp[S[V[i]][j]] + (SS - j) + ps[i] > x) {
				c++;
			} else break;
		}
		//cerr << c << '\n';
		if(c > i + 1) return false;
	}
	
	//cerr << "!!!" << x << '\n';
	return (c <= x);
}

int main(){
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	ll n;
	cin >> n >> t >> m;
	ll u, v;
	for(int i = 1; i < n; i++){
		cin >> u >> v;
		G[u].pb(v);
		G[v].pb(u);
	}
	DFS(t, -1);
	
	
	ll sz = V.size();
	dp2[sz-1] = 0;
	ll sm = 0;
	ps[sz-1] = 0;
	for(int i = sz - 2; i >= 0; i--){
		ps[i] = sm;
		sm += son[V[i]];
		
		//cerr << son[V[i]] << '\n';
		ll K = 0;
		sort(S[V[i]].begin(), S[V[i]].end(), CMP);
		for(auto ch : S[V[i]]){
			//cerr << '!' << ch << ' ' << dp[ch] << ' ' << sm << '\n';
			A.pb({dp[ch] + sm - K, i + 1});
			K ++;
		}
		
		dp2[i] = min( max(dp2[i + 1], sm-son[V[i]] + m1[V[i]] + son[V[i]]), 1LL + max(dp2[i + 1], sm-son[V[i]] + m2[V[i]] + son[V[i]] - 1) );
		
	}
	sort(A.begin(), A.end()); reverse(A.begin(), A.end());
	ll M = A.size();
	ll cnt = 1;
	//cerr << '\n';
	//dp2[0] = 100000000;
	/*
	ll ans = min(dp2[0], (M > 0 ? A[0].F : 0));
	bool fl=true;;
	A.pb({0, 0});
	for(int i = 0; i < M; i++){
		for(int j = A[i].S; j <= n; j++){
			C[j] ++;
			if(C[j] > j) fl = false;
		}
		//cerr << i << " " << fl << '\n';
		if(fl) ans = min(ans, i + 1 + A[i + 1].F);
		cerr << i + 1 + A[i + 1].F << '\n';
	}
	cout << ans << '\n';
	*/
	//cout << dp2[0] << '\n';
	ll l = -1, r = n, mid;
	while(l + 1 < r){
		mid = (l + r) >> 1;
		if(check(mid)) r = mid;
		else l = mid;
	} 
	//cerr << check(1) << '\n';
	cout << r;
	return 0;
}
/*
5 1 2
1 2
2 3
2 4
3 5

10 1 4
1 2
2 3
2 4
3 9
3 5
4 7
4 6
6 8
7 10

7 1 3
1 2
2 3
2 4
4 5
2 6
6 7


*/

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:109:5: warning: unused variable 'M' [-Wunused-variable]
  ll M = A.size();
     ^
mousetrap.cpp:110:5: warning: unused variable 'cnt' [-Wunused-variable]
  ll cnt = 1;
     ^~~

• Subtask 1: 20 / 20
• Subtask 2: 25 / 25
• Subtask 3: 20 / 20
• Subtask 4: 35 / 35