Submission #307516

#	Time	Username	Problem	Language	Result	Execution time	Memory
307516		tengiz05	Race (IOI11_race)	C++17	100 / 100	1351 ms	36076 KiB

race

#include "race.h"
#include <bits/stdc++.h>
using namespace std;
const int NN = 2e5 + 5;
bool used[NN];
int sz[NN];
int n, k;
vector<pair<int, int>> edges[NN];
void dfs_size(int u, int p){
	sz[u] = 1;
	for(auto X : edges[u]){
		int v = X.first;
		if(used[v] || v == p)continue;
		dfs_size(v, u);
		sz[u] += sz[v];
	}
}
int centroid(int u, int p, int size){
	for(auto X : edges[u]){
		int v = X.first;
		if(used[v] || v == p)continue;
		if(sz[v] > size/2)return centroid(v, u, size);
	}
	return u;
}
vector<pair<int, int>> m;
map<int, int> len;
void dfs(int u, int p, int dist, int t){
	if(dist > k)return;
	m.push_back({dist, t});
	for(auto X : edges[u]){
		int v = X.first;
		int cost = X.second;
		if(used[v] || v == p)continue;
		dfs(v, u, dist+cost, t+1);
	}
}
void dfs2(int u, int p, int dist, int t){
	if(dist > k)return;
	if(!len.count(dist))len[dist] = t;
	else len[dist] = min(len[dist], t);
	for(auto X : edges[u]){
		int v = X.first;
		int cost = X.second;
		if(used[v] || v == p)continue;
		dfs2(v, u, dist+cost, t+1);
	}
}

int find_min(int u, int p=-1){
	int ans = 1e9;
	len.clear();
	dfs_size(u, u);
	u = centroid(u, u, sz[u]);
	len[0] = 0;
	used[u] = true;//delete centroid
	for(auto X : edges[u]){
		m.clear();
		int v = X.first;
		int cost = X.second;
		if(used[v])continue;
		dfs(v, u, cost, 1);
		for(auto X : m){
			int dist = X.first;
			int time = X.second;
			if(len.count(k-dist)){
				ans = min(ans, len[k-dist]+time);
			}//cout << dist << ' ' << time << '\n';
		}
		dfs2(v, u, cost, 1);
	}
	for(auto X : edges[u]){
		int v = X.first;
		if(used[v] || p == v)continue;
		ans = min(ans, find_min(v, u));
	}
	return ans;
}
int best_path(int N, int K, int H[][2], int L[]){
	n = N;
	k = K;
	for(int i=0;i<n-1;i++){
		edges[H[i][0]].push_back({H[i][1],L[i]});
		edges[H[i][1]].push_back({H[i][0],L[i]}); 
	}
	if(k == 0){
		return 0;
	}
	int ans = find_min(0);
//	cout << '\n' << ans << '\n';
	if(ans == 1e9)ans = -1;
	return ans;
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 57 / 57