cf1076d 贪心最短路

Posted 2021-02-09 zsben991126

#include<bits/stdc++.h>
#include<queue>
using namespace std;
#define maxn 300005
#define ll long long
struct qnode{
    ll v,c,id;
    qnode(){}
    qnode(ll v,ll c,ll id):v(v),c(c),id(id){}
    bool operator<(const qnode&r)const{
        return c>r.c;
    }
};
struct Edge{ll to,nxt,w,id;}edge[maxn<<1];
ll n,m,k,head[maxn],tot,vis[maxn],dist[maxn];
void init(){
    tot=0;
    memset(head,-1,sizeof head);
}
void addedge(ll u,ll v,ll w,ll id){
    edge[tot].to=v;edge[tot].nxt=head[u];edge[tot].id=id;edge[tot].w=w;head[u]=tot++;
}

priority_queue<qnode>pq;
vector<ll>vec;
void dijkstra(ll s){
    memset(vis,0,sizeof vis);
    memset(dist,0x3f,sizeof dist);
    dist[s]=0;
    pq.push(qnode(s,0,0));
    while(!pq.empty()){
        qnode tmp=pq.top();
        pq.pop();
        ll u=tmp.v;
        if(vis[u])continue;
        vis[u]=1;
        vec.push_back(tmp.id);
        if(vec.size()==k+1)return;
        for(int i=head[u];i!=-1;i=edge[i].nxt){
            ll v=edge[i].to,cost=edge[i].w;
            if(vis[v])continue;
            if(dist[v]>dist[u]+cost){
                dist[v]=dist[u]+cost;
                pq.push(qnode(v,dist[v],edge[i].id));
            }
        }
    }
}

int main(){
    init();
    int u,v,w;
    cin>>n>>m>>k;
    for(int i=1;i<=m;i++){
        cin>>u>>v>>w;
        addedge(u,v,w,i);
        addedge(v,u,w,i);
    }
    dijkstra(1);
    
    k=min(k,n-1);
    cout<<k<<endl;
    for(int i=1;i<=k;i++)
        cout<<vec[i]<<" ";
return 0;
}