Submission #585121

#	Time	Username	Problem	Language	Result	Execution time	Memory
585121		amunduzbaev	Mousetrap (CEOI17_mousetrap)	C++17	0 / 100	310 ms	66800 KiB

mousetrap

#include "bits/stdc++.h"
using namespace std;
 
#define ar array
typedef int64_t ll;
//~ #define int ll
 
const int N = 1e6 + 5;
vector<int> edges[N];
int n, t, m, dp[N], is[N];
int c[N];
 
void dfs(int u, int p = -1){
	is[u] = (u == t), c[u] = -1;
	vector<int> t;
	for(auto x : edges[u]){
		if(x == p) continue;
		dfs(x, u);
		is[u] |= is[x];
		if(!is[x]) t.push_back(x);
		else c[u] = x;
	}
	sort(t.begin(), t.end(), [&](int& i, int& j){
		return dp[i] > dp[j];
	});
	edges[u] = t;
	
	if(t.empty()) dp[u] = 0;
	else {
		dp[u] = t.size();
		if((int)t.size() > 1) dp[u] += dp[t[1]]; 
	}
}
 
signed main(){
	ios::sync_with_stdio(0); cin.tie(0);
	
	cin>>n>>t>>m;
	if(t == m){
		cout<<0<<"\n";
		return 0;
	}
	for(int i=1;i<n;i++){
		int a, b; cin>>a>>b;
		edges[a].push_back(b);
		edges[b].push_back(a);
	}
	
	dfs(m);
	int tot = 0, u = m;
	vector<int> v;
	while(u != t){
		v.push_back(edges[u].size());
		tot += edges[u].size();
		u = c[u];
	}
	
	for(int i=(int)v.size() - 2;~i;i--){
		v[i] += v[i+1];
	}
	auto check = [&](int mx){
		int u = m, pos = 0, prev = 0, in = 0;
		while(u != t){
			pos++;
			for(auto x : edges[u]){
				if(dp[x] + prev + v[in] > mx) pos--, prev++;
			}
			if(pos < 0) return false;
			u = c[u];
		}
		
		return true;
	};
	
	int l = tot, r = 1e9;
	while(l < r){
		int m = (l + r) >> 1;
		if(check(m)) r = m;
		else l = m + 1;
	}
	
	//~ while(m != t){
		//~ pos++;
		//~ vector<int>& t = edges[m];
		//~ sort(t.begin(), t.end(), [&](int& i, int& j){
			//~ return dp[i] > dp[j];
		//~ });
		
		//~ if(pos >= (int)t.size()){
			//~ pos -= (int)t.size();
			//~ res += (int)t.size();
		//~ } else {
			//~ res += dp[t[pos]] + (int)t.size();
			//~ pos = 1e9;
		//~ }
		//~ m = c[m];
	//~ }
	
	cout<<l<<"\n";
}
 
/*
 
8 7 1
1 2
2 3
3 4
3 5
3 6
4 7
4 8
 
*/

• Subtask 1: 0 / 20
• Subtask 2: 0 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35