Submission #835907

#	Time	Username	Problem	Language	Result	Execution time	Memory
835907		Juan	Commuter Pass (JOI18_commuter_pass)	C++17	100 / 100	442 ms	44276 KiB

commuter_pass

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define tii tuple<int, int, int>
#define pii pair<int, int>
#define ff first
#define ss second
const int maxn = 1e5 + 5, INF = 0x3f3f3f3f3f3f3f3f;

vector<pii> adj[maxn];
vector<int> g[maxn];
vector<tii> edges;

vector<int> dijkstra(int ini){
	priority_queue<pii, vector<pii>, greater<pii>> pq;
	vector<int> dist(maxn, INF);
	dist[ini] = 0;
	pq.push({0, ini});

	while(pq.size()){
		auto[d, u] = pq.top();
		pq.pop();
		if(d > dist[u]) continue;

		for(auto [v, w] : adj[u]) if(dist[u]+w < dist[v]){
			dist[v] = dist[u] + w;
			pq.push({dist[u]+w, v});
		}
	}

	return dist;
}

int solve(int ini, int fim){
	int ans = -1;
	priority_queue<tii, vector<tii>, greater<tii>> pq;
	int dist[maxn][3];
	//dist[u][0,1,2] = didnt enter sp, in sp, out of sp | sp = short path
	for(int i = 0; i < maxn; i++){
		dist[i][0] = dist[i][1] = dist[i][2] = INF;
	}
	dist[ini][0] = 0;
	pq.push({0, ini, 0});

	while(pq.size()){
		auto[d, u, tp] = pq.top();
		pq.pop();
		if(d > dist[u][tp]) continue;
		if(u==fim) {ans = d; break;}

		//enter/continue in sp ---> 0 or 1 (didnt or in)
		if(tp==0 || tp==1) for(int v : g[u]) if(dist[v][1] > d){
			dist[v][1] = d;
			pq.push({d, v, 1});
		}

		//get out ---> 1 (in)
		if(tp==1){
			for(auto [v, w] : adj[u]) if(dist[v][2] > d+w){
				dist[v][2] = d+w;
				pq.push({d+w, v, 2});
			}			
		} // continue out ---> 0 or 2 (didnt or out)
		else for(auto [v, w] : adj[u]) if(dist[v][tp] > d+w){
			dist[v][tp] = d+w;
			pq.push({d+w, v, tp});
		}
	}

	return ans;
}

int32_t main(){
	int n, m; cin >> n >> m;
	int S, T; cin >> S >> T;
	int U, V; cin >> U >> V;
	for(int i = 0; i < m; i++){
		int a, b, c; cin >> a >> b >> c;
		adj[a].push_back({b, c});
		adj[b].push_back({a, c});
		edges.push_back({a, b, c});
		edges.push_back({b, a, c});
	}

	vector<int> distS = dijkstra(S), distT = dijkstra(T);
	int minpath = distS[T];

	for(auto[a, b, c] : edges){
		if(distS[a]+c+distT[b] == minpath){
			g[a].push_back(b);
		}
	}
	int ans = solve(U,V);

	for(int i = 1; i <= n; i++) g[i].clear();
	for(auto[a, b, c] : edges){
		if(distS[a]+c+distT[b] == minpath){
			g[b].push_back(a);
		}
	}
	ans = min(ans, solve(U,V));

	cout << ans << '\n';
}

• Subtask 1: 16 / 16
• Subtask 2: 15 / 15
• Subtask 3: 24 / 24
• Subtask 4: 45 / 45