最小生成树prim+邻接表优化

#include <iostream>  #include <algorithm>   #include <string.h> #include <queue> using namespace std;  const int inf=0x3f3f3f3f;;const int maxx=1e3+100;;const int maxn=2e6+10;typedef long long ll;int m,n,q,ans,sum;  int dis[maxx];int sto[maxx];int head[2*maxn];bool vis[maxx]; int a[maxx][maxx];struct  point{        int to;      int next; int val; bool operator < (const point &a) const{return val>a.val;}};  point pt[2*maxn]; void add(int u,int v,int val){      pt[q].next=head[u];            pt[q].to=v;  pt[q].val=val;  head[u]=q++;} void prim(int st)  {      priority_queue<point>q;    point t1,t2;int w,v;    memset(dis,inf,sizeof(dis));    memset(vis,false,sizeof(vis));    for (int i=head[st];i!=-1;i=pt[i].next)    {     int v=pt[i].val;     if (dis[pt[i].to]>v)     {     dis[pt[i].to]=v;     t1.to=pt[i].to;     t1.val=v;     q.push(t1); }}vis[st]=true;ans=1;sum=0;while (!q.empty()){point t=q.top();q.pop();int v=t.to;if (vis[v])continue;vis[v]=true;sum+=dis[v];ans++;for (int i=head[v];i!=-1;i=pt[i].next){ int u=pt[i].to; if (!vis[u]&&pt[i].val<dis[u]) { dis[u]=pt[i].val; t2.to=u; t2.val=pt[i].val; q.push(t2); }}}}int main(){int k,u,v,val,st;cin>>m>>n>>k;memset(head,-1,sizeof(head));q=1;for (int i=0;i<m;i++){cin>>u>>v>>val;add(u,v,val);add(v,u,val);st=u;}    prim(st);     if (ans==n)    cout<<sum<<endl;    else    cout<<"don't exit "<<endl; //没有return 0;}