P2763: [JLOI2011]飞行路线

然而WA了呀，这道分层图，也是不明白为什么WA了=-=

 const maxe=; maxn=; points=;
 type
   node=record
     f,t,l:longint;
   end;
 var n,m,k,i,j,u,v,x,s,t,num:longint;
 b:array[..maxe] of node;
 ans:int64;
 f:array[..] of longint;
 p:array[..points] of boolean;
 head:array[..points] of longint;
 d:array[..points] of int64;
 procedure insert(u,v,x:longint);
 begin
   inc(num);
   b[num].f:=head[u];
   b[num].t:=v;
   b[num].l:=x;
   head[u]:=num;
 end;
 procedure spfa;
 var now,nowe,l,r,v:longint;
 begin
   for l:= to points do d[l]:=maxn;
   fillchar(p,sizeof(p),true);
   l:=; r:=; f[]:=s; d[s]:=; p[s]:=false; ans:=maxn; //writeln(ans);
   while l<=r do
     begin
       now:=f[l];
       nowe:=head[now];
       while nowe<> do
         begin
           v:=b[nowe].t;
           if d[now]+b[nowe].l<d[v] then
             begin
               d[v]:=d[now]+b[nowe].l;
               if p[v] then
                 begin
                   p[v]:=false;
                   inc(r);
                   f[r]:=v;
                 end;
               //if ((v mod k)=t) and (d[v]<ans) then ans:=d[v];
             end;
           nowe:=b[nowe].f;
         end;
       inc(l);
       p[now]:=true;
     end;
   for l:= to k do
     if ans>d[l*n+t] then ans:=d[l*n+t];
 end;
 begin
   readln(n,m,k);
   readln(s,t);
   inc(s); inc(t);
   for i:= to m do
     begin
       readln(u,v,x);
       inc(u); inc(v);
       for j:= to k do
         begin
           insert(u+j*n,v+j*n,x);
           insert(v+j*n,u+j*n,x);
           if j<>k then
             begin
               insert(u+j*n,v+(j+)*n,);
               insert(v+j*n,u+(j+)*n,);
             end;
         end;
     end;
   spfa;
   if ans=maxn then writeln()
     else writeln(ans);
 end.

暂且先不管为什么WA吧，首先这是个分层图原图既然是一层的。我们把它拆成k+1层。每一条边既能连本层，也能连到下一层。然后直接裸上Dijikstra即可，而spfa大概也是可以的吧。

而这是正解

 #include <queue>
 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 #define N 1200100
 using namespace std;
 int n,m,k;
 int st,ed,cnt;
 int head[N];
 int dis[N];
 int v[N];
 struct node
 {
     int from,to,val,next;
 }edge[N<<];
 struct element
 {
     int val,no;
 };
 bool operator < (element a,element b)
 {
     if(a.val==b.val)return a.no<b.no;
     return a.val>b.val;
 }
 priority_queue<element>q;
 void dijikstra(int s,int e)
 {
     memset(dis,0x3f,sizeof(dis));
     element fir;
     fir.val=,fir.no=s;
     dis[s]=;
     q.push(fir);
     while(!q.empty())
     {
         element u=q.top();
         q.pop();
         if(v[u.no])continue;
         v[u.no]=;
         for(int i=head[u.no];i!=-;i=edge[i].next)
         {
             int to=edge[i].to;
             if(dis[u.no]+edge[i].val<dis[to])
             {
                 dis[to]=dis[u.no]+edge[i].val;
                 element pus;
                 pus.no=to,pus.val=dis[to];
                 q.push(pus);
             }
         }
     }
     int ans=0x3f3f3f3f;
     for(int i=;i<=k;i++)
     {
         ans=min(ans,dis[e+i*n]);
     }
     printf("%d\n",ans);
 }
 void init()
 {
     memset(head,-,sizeof(head));
     cnt=;
 }
 void edgeadd(int from,int to,int val)
 {
     edge[cnt].from=from;
     edge[cnt].to=to;
     edge[cnt].val=val;
     edge[cnt].next=head[from];
     head[from]=cnt++;
 }

 int main()
 {
     init();
     scanf("%d%d%d",&n,&m,&k);
     scanf("%d%d",&st,&ed);
     st++,ed++;
     for(int i=;i<=m;i++)
     {
         int x,y,z;
         scanf("%d%d%d",&x,&y,&z);
         x++,y++;
         for(int i=;i<=k;i++)
         {
             edgeadd(x+i*n,y+i*n,z);
             edgeadd(y+i*n,x+i*n,z);
             if(i!=k)
             {
                 edgeadd(x+i*n,y+(i+)*n,);
                 edgeadd(y+i*n,x+(i+)*n,);
             }
         }
     }
     dijikstra(st,ed);
 }