求助

#define int long long//__int128
int n,m,s,u,v,d,i,fl[300001],dis[300001],id[300001],head[300001],vis[300001],cnt;
struct edge{
    int to,dis,next;
}e[600001];
void add_edge(int u,int v,int d,int t){
    cnt++;
    id[cnt]=t;
    e[cnt].dis=d;
    e[cnt].to=v;
    e[cnt].next=head[u];
    head[u]=cnt;
}
struct node{
    int dis,pos;
    bool operator <(const node &x)const{
        return x.dis<dis;
    }
};
vector<int>ans;
priority_queue<node>q;
void dfs(int x){
	fl[x]=1;
	for(i=head[x];i;i=e[i].next){
		int y=e[i].to;
		if(!fl[y]&&dis[y]==dis[x]+e[i].dis){
			if(ans.size()<s) ans.push_back(id[i]);
			dfs(y);
		}
	}
}
signed main(){
	cin>>n>>m>>s;
	for(i=1;i<=n;i++) dis[i]=1e9;
	for(i=1;i<=m;i++){
		cin>>u>>v>>d;
		add_edge(u,v,d,i);
		add_edge(v,u,d,i);
	}
	dis[1]=0;
	q.push((node){0,1});
	while(!q.empty()){
		node tmp=q.top();
		q.pop();
		int x=tmp.pos,d=tmp.dis;
		if(!vis[x]){
			vis[x]=1;
			for(i=head[x];i;i=e[i].next){
				int y=e[i].to;
				if(dis[y]>dis[x]+e[i].dis){
					dis[y]=dis[x]+e[i].dis;
					q.push((node){dis[y],y});
				}
			}
		}
	}
	dfs(1);
	cout<<ans.size()<<endl;
	for(auto x:ans) cout<<x<<" ";
}