Submission #1022496

#	Time	Username	Problem	Language	Result	Execution time	Memory
1022496		sinatbtfard	Commuter Pass (JOI18_commuter_pass)	C++17	100 / 100	533 ms	39340 KiB

commuter_pass

#include <bits/stdc++.h>
 
#define ll long long
#define pb push_back
 
using namespace std;
 
const int maxn = 1e5 + 1;

int n, m, S, T, U, V;
ll dist[2][maxn], dist2[4][maxn];
vector <pair <int, ll>> adj[maxn];
set <pair <ll, int>> s;
set <vector <ll>> s2;
 
void dijkstra (int src, int x){
	fill(dist[x], dist[x] + n + 1, 1e15);
	dist[x][src] = 0;
	s.insert({dist[x][src], src});
	for (int i = 0; i < n; i++){
		int v = (*s.begin()).second;
		s.erase(s.begin());
		for (auto [u, w] : adj[v]){
			if (dist[x][u] <= dist[x][v] + w)
				continue;
			s.erase({dist[x][u], u});
			dist[x][u] = dist[x][v] + w;
			s.insert({dist[x][u], u});
		}
		if (!s.size())
			break;
	}
}
 
void dijkstra2 (){
	for (int i = 0; i < 4; i++)
		fill(dist2[i], dist2[i] + n + 1, 1e15);
	dist2[0][U] = 0;
	s2.insert({0, U, 0});
	while (s2.size()){
		vector <ll> x = (*s2.begin());
		ll v = x[1], st = x[2];
		s2.erase(s2.begin());
		if (st == 0){
			for (auto [u, w] : adj[v]){
				// check whether we go through the shortest subpath in the opposing direction as s does or not
				if (dist[0][v] + dist[1][u] + w == dist[0][T]){
					if (dist2[1][u] <= dist2[st][v])
						continue;
					dist2[1][u] = dist2[st][v];
					s2.insert({dist2[1][u], u, 1});
				}
				if (dist[1][v] + dist[0][u] + w == dist[0][T]){
					if (dist2[2][u] <= dist2[st][v])
						continue;
					dist2[2][u] = dist2[st][v];
					s2.insert({dist2[2][u], u, 2});
				}
			}
			for (auto [u, w] : adj[v]){
				// we choose not to enter through the shortest path node or the node is not a part of a shortest path 
				if (dist2[0][u] <= dist2[st][v] + w)
					continue;
				dist2[0][u] = dist2[st][v] + w;
				s2.insert({dist2[0][u], u, 0});
			}
		}
		if (st == 1){
			// state where we go in the same flow as s to t (s -> t)
			for (auto [u, w] : adj[v]){
				if (dist[0][v] + dist[1][u] + w == dist[0][T]){
					if (dist2[1][u] <= dist2[st][v])
						continue;
					dist2[1][u] = dist2[st][v];
					s2.insert({dist2[1][u], u, 1});
				}
				else{
					if (dist2[3][u] <= dist2[st][v] + w)
						continue;
					dist2[3][u] = dist2[st][v] + w;
					s2.insert({dist2[3][u], u, 3});
				}
			}
		}
		if (st == 2){
			// state where we go in the opposing flow (t -> s)
			for (auto [u, w] : adj[v]){
				if (dist[1][v] + dist[0][u] + w == dist[0][T]){
					if (dist2[2][u] <= dist2[st][v])
						continue;
					dist2[2][u] = dist2[st][v];
					s2.insert({dist2[2][u], u, 2});
				}
				else{
					if (dist2[3][u] <= dist2[st][v] + w)
						continue;
					dist2[3][u] = dist2[st][v] + w;
					s2.insert({dist2[3][u], u, 3});
				}
			}
		}
		if (st == 3){
			// state where we have finished making use of s -> t
			for (auto [u, w] : adj[v]){
				if (dist2[3][u] <= dist2[st][v] + w)
					continue;
				dist2[3][u] = dist2[st][v] + w;
				s2.insert({dist2[3][u], u, 3});
			}
		}
	}
}
 
int main (){
	ios_base::sync_with_stdio(0);
	cin >> n >> m >> S >> T >> U >> V;
	for (int x, y, z, i = 0; i < m; i++){
		cin >> x >> y >> z;
		adj[x].pb({y, z});
		adj[y].pb({x, z});
	}
	dijkstra(S, 0);
	dijkstra(T, 1);
	dijkstra2();
	cout << min({dist2[0][V], dist2[1][V], dist2[2][V], dist2[3][V]});
}

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