제출 #502485

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
502485		PoPularPlusPlus	Torrent (COI16_torrent)	C++17	0 / 100	163 ms	36576 KiB

torrent

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long 
#define pb(e) push_back(e)
#define sv(a) sort(a.begin(),a.end())
#define sa(a,n) sort(a,a+n)
#define mp(a,b) make_pair(a,b)
#define vf first
#define vs second
#define ar array
#define all(x) x.begin(),x.end()
const int inf = 0x3f3f3f3f;
const int mod = 1000000007; 
const double PI=3.14159265358979323846264338327950288419716939937510582097494459230;
bool remender(ll a , ll b){return a%b;}

const int N = 300006;

vector<int> adj[N];
bool vis[N];
int par[N];
int mx[N];
vector<int> v[N];
int a , b;
int adj1[N];

void dfss(int node){
	vis[node] = 1;
	mx[node] = 0;
	for(int i : adj[node]){
		if(!vis[i] && i != par[node]){
			dfss(i);
			v[node].pb(mx[i]);
		}
	}
	sv(v[node]);
	int chances = 0;
	for(int i = v[node].size()-1; i >= 0; i--){
		chances++;
		mx[node] = max(mx[node] , chances + v[node][i]);
	}
}

void dfs(int node){
	vis[node] = 1;
	for(int i : adj[node]){
		if(!vis[i]){
			par[i] = node;
			dfs(i);
		}
	}
}

void dfs1(int node , int done , int total){
	if(node == a)return;
	if(done + mx[node] > total)return;
	vis[node] = 1;
	if(v[node].size() == 0){
		if(vis[par[node]] == 0)dfs1(par[node] , done + 1 , total);
		return;
	}
	int p[v[node].size()];
	p[0] = v[node][0] + v[node].size() - 1;
	for(int i = 1; i < (int) v[node].size(); i++){
		p[i] = max(p[i-1] , v[node][i] + (int)v[node].size() - (i + 1));
	}
	for(int i = v[node].size() - 1; i >= 0 && done < total; i--){
		if(p[i] + 2 + done <= total && vis[par[node]] == 0){
			dfs1(par[node] , done + 1 , total);
			return;
		}
		done++;
	}
	if(done < total)dfs1(par[node] , done + 1 , total);
}

void dfs2(int node , int done , int total){
	if(node == b)return;
	if(done + mx[node] > total)return;
	vis[node] = 1;
	int nex = adj1[node];
	if(vis[nex])return;
	if(v[node].size() == 0){
		dfs2(nex , done + 1 , total);
		return;
	}
	int p[v[node].size()];
	p[0] = v[node][0] + v[node].size() - 1;
	for(int i = 1; i < (int) v[node].size(); i++){
		p[i] = max(p[i-1] , v[node][i] + (int)v[node].size() - (i + 1));
	}
	for(int i = v[node].size() - 1; i >= 0 && done < total; i--){
		if(p[i] + 2 + done <= total && vis[nex] == 0){
			dfs1(nex , done + 1 , total);
			return;
		}
		done++;
	}
	if(done < total)dfs1(nex , done + 1 , total);
}

void solve(){
	int n;
	cin >> n;
	cin >> a >> b;
	for(int i = 0; i < n - 1; i++){
		int x , y;
		cin >> x >> y;
		adj[x].pb(y);
		adj[y].pb(x);
	}
	memset(vis,0,sizeof vis);
	dfs(a);
	par[a] = -1;
	vector<int> path;
	int cur = b;
	while(cur != a){
		cur = par[cur];
		if(cur == a)break;
		path.pb(cur);
	}
	if(path.size() == 0)adj1[a] = b;
	else {
		adj1[a] = path.back();
		adj1[path[0]] = b;
		for(int i = 0; i < (int)path.size() - 1; i++){
			adj1[path[i + 1]] = path[i];
		}
	}
	memset(vis,0,sizeof vis);
	dfss(b);
	for(int i : path)dfss(i);
	dfss(a);
	int l = max(mx[a] , mx[b]) , r = n;
	//cout << l << '\n';
	int ans = - 1;
	while(l <= r){
		int mid = (l + r)/2;
		memset(vis,0,sizeof vis);
		dfs1(b , 0 , mid);
		dfs2(a , 0 , mid);
		int possible = 1;
		for(int i : path){
			if(vis[i] == 0)possible = 0;
		}
		if(possible == 1){
			ans = mid;
			r = mid - 1;
		}
		else l = mid + 1;
	}
	cout << ans << '\n';
}

int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//freopen("dec.in", "r", stdin);
//freopen("dec.out", "w", stdout);
	//int t;cin >> t;while(t--)
	solve();
	return 0;
}

• Subtask 1: 0 / 31
• Subtask 2: 0 / 69