Submission #698102

#	Time	Username	Problem	Language	Result	Execution time	Memory
698102		myrcella	Olympic Bus (JOI20_ho_t4)	C++17	0 / 100	29 ms	2004 KiB

ho_t4

//by szh
#include<bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define pii pair<int,int>
#define pll pair<long long,long long>
#define pb push_back
#define debug(x) cerr<<#x<<"="<<x<<endl
#define pq priority_queue
#define inf 0x3f
#define rep(i,a,b) for (int i=a;i<(b);i++)
#define MP make_pair
#define SZ(x) (int(x.size()))
#define ll long long
#define mod 1000000007
#define ALL(x) x.begin(),x.end()
void inc(int &a,int b) {a=(a+b)%mod;}
void dec(int &a,int b) {a=(a-b+mod)%mod;}
int lowbit(int x) {return x&(-x);}
ll p0w(ll base,ll p) {ll ret=1;while(p>0){if (p%2ll==1ll) ret=ret*base%mod;base=base*base%mod;p/=2ll;}return ret;}

const int maxn = 50010;
int dis[222][222];
int dist[222];
bool vis[222];

int n,m,big;

struct EDGE{
	int u,v,c,d;
} e[maxn];
vector <int> redge[222],edge[222];
pq <pii,vector<pii>,greater<pii> > q;

int ans = 2e9;
bool used[maxn];
vector <int> usededge;


int dijkstra(int st,int ed,int rev) {
	memset(dist,inf,sizeof(dist));
	dist[st] = 0;
	while (!q.empty()) q.pop();
	q.push({0,st});
	while (!q.empty()) {
		pii cur = q.top();
		q.pop();
		if (dist[cur.se]!=cur.fi) continue;
		int u = cur.se;
		if (u==ed) return cur.fi;
		for (int i:edge[u]) {
			int v=e[i].v;
			if (i==rev) {
				if (e[i].u==u) continue;
				else v = e[i].u;
			}
			if (dist[v] > dist[u] + e[i].c) {
				dist[v] = dist[u] + e[i].c;
				q.push({dist[v],v});
			}
		}
	}
	return big;
} 

bool dfs(int st,int ed,int u) {
	vis[u]=true;
	if (u==ed) return true;
	for (int i:edge[u]) {
		int v=e[i].v;
		if (!vis[v] and dis[st][u] + e[i].c + dis[v][ed]==dis[st][ed] and dfs(st,ed,v)) {
			usededge.pb(i);
			used[i]=true;
			return true;
		}
	}
	return false;
}

void solve(int id) {
	//0: n->1 used the inverted edge 
	//find the shortest path
	int st = 1, ed = n;
	if (id==1) swap(st,ed);
	if (dis[st][ed]==big) return;
	int cur = st;
	rep(i,1,n+1) vis[i]=false;
	dfs(st,ed,cur);
	rep(i,0,m) {
		if (dis[ed][e[i].v]==big or dis[e[i].u][st]==big) continue;
		int tmp = dis[st][ed];
		if (used[i]) {
			edge[e[i].v].pb(i);
			tmp = dijkstra(st,ed,i);
			edge[e[i].v].pop_back();
			if (tmp==big) continue;
		}
		ans = min(ans,dis[ed][e[i].v] + e[i].d + e[i].c + dis[e[i].u][st] + tmp);
		
	}
		
	while (!usededge.empty()) used[usededge.back()] = false,usededge.pop_back();
}

int main() {
//	freopen("input.txt","r",stdin);	
	std::ios::sync_with_stdio(false);cin.tie(0);
	
	cin>>n>>m;
	memset(dis,inf,sizeof(dis));
	big = dis[0][0];
	rep(i,1,n+1) dis[i][i] =0 ;
	rep(i,0,m) {
		cin>>e[i].u>>e[i].v>>e[i].c>>e[i].d;
		dis[e[i].u][e[i].v] = min(dis[e[i].u][e[i].v],e[i].c);
		redge[e[i].v].pb(i); 
		edge[e[i].u].pb(i);
	}
	rep(k,1,n+1)
		rep(i,1,n+1)
			rep(j,1,n+1) dis[i][j] = min(dis[i][k] + dis[k][j],dis[i][j]);
//	debug(ans);
	solve(0);
	solve(1);
//	debug(ans);
	ans = min(ans,dis[1][n]+dis[n][1]);
	if (ans==2e9) cout<<-1;
	else cout<<ans;
	
	return 0;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 11
• Subtask 3: 0 / 21
• Subtask 4: 0 / 63