Submission #207392

#	Time	Username	Problem	Language	Result	Execution time	Memory
207392		Saboon	Commuter Pass (JOI18_commuter_pass)	C++14	100 / 100	587 ms	27300 KiB

commuter_pass

#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
 
const int maxn = 1e5 + 10;
const int inf = 1e9;
 
int n, m;
vector<pair<int,ll>> g[maxn];
vector<int> G[maxn];
ll dp[maxn], pd[maxn];

bool mark[maxn];
int Q[maxn], tail, head;
vector<int> builddag(int s, int t){
	tail = 0, head = 0;
	mark[t] = 1, Q[head ++] = t;
	vector<int> ret;
	while (tail < head){
		int v = Q[tail ++];
		ret.push_back(v);
		for (auto ed : g[v]){
			int u = ed.first, w = ed.second;
			if (!mark[u] and dp[u] + w == dp[v])
				mark[u] = 1, Q[head ++] = u;
			if (dp[u] + w == dp[v])
				G[v].push_back(u);
		}
	}
	sort(ret.begin(), ret.end(), [] (int v, int u){ return dp[v] < dp[u];} );
	return ret;
}

void dijkstra(int src){
	memset(dp, 63, sizeof dp);
	dp[src] = 0;
	set<pair<ll,int>> s;
	s.insert({dp[src], src});
	while (!s.empty()){
		int v = (*s.begin()).second;
		s.erase(s.begin());
		for (auto ed : g[v]){
			int u = ed.first, w = ed.second;
			if (dp[u] > dp[v] + w){
				s.erase({dp[u], u});
				dp[u] = dp[v] + w;
				s.insert({dp[u], u});
			}
		}
	}
}

ll dpfr[maxn], dpto[maxn];

int main(){
	ios_base::sync_with_stdio(false);
	int m;
	int s, t;
	int fr, to;
	cin >> n >> m >> s >> t >> fr >> to;
	for (int i = 0; i < m; i++){
		int v, u, c;
		cin >> v >> u >> c;
		g[v].push_back({u, c});
		g[u].push_back({v, c});
	}
	dijkstra(fr); // keep shortest path data in dp
	for (int i = 1; i <= n; i++)
		dpfr[i] = dp[i];
	dijkstra(to); // keep shortest path data in dp
	for (int i = 1; i <= n; i++)
		dpto[i] = dp[i];
	dijkstra(s); // keep shortest path data in dp
	ll answer = dpfr[to];
	vector<int> tpl = builddag(s, t); // topological sort of shortest path's DAG s to t 
	for (int i = 0; i < (int)tpl.size(); i++){
		int v = tpl[i];
		dp[v] = dpfr[v], pd[v] = dpto[v];
		for (auto u : G[v]){
			dp[v] = min(dp[v], dp[u]);
			pd[v] = min(pd[v], pd[u]);
		}
		ll now = min(dp[v] + dpto[v], pd[v] + dpfr[v]);
		if (answer == -1 or answer > now)
			answer = now;
	}
	cout << answer << '\n';
}

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