【最短路】【Heap-Dijkstra】【分层图】bzoj2662 [BeiJing wc2012]冻结

裸的分层图最短路。

#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;
#define N 51
#define K 51
#define M 2001
struct Point{int u,d;Point(const int &a,const int &b){d=a;u=b;}Point(){}};
bool operator < (const Point &a,const Point &b){return a.d>b.d;}
priority_queue<Point>q;
int n,m,k,dis[N*K],ans=2147483647;
bool vis[N*K];
int first[M*K*2],next[M*K*2],v[M*K*2],w[M*K*2],en,x,y,z;
void AddEdge(const int &U,const int &V,const int &W)
{
    v[++en]=V;
    w[en]=W;
    next[en]=first[U];
    first[U]=en;
}
void dijkstra(const int &s)
{
    memset(dis,0x7f,sizeof(dis));
    dis[s]=0; q.push(Point(0,s));
    while(!q.empty())
      {
        Point x=q.top(); q.pop();
        if(!vis[x.u])
          {
            vis[x.u]=0;
            for(int i=first[x.u];i;i=next[i])
              if(dis[v[i]]>dis[x.u]+w[i])
                {
                  dis[v[i]]=dis[x.u]+w[i];
                  q.push(Point(dis[v[i]],v[i]));
                }
          }
      }
    for(int i=0;i<=k;i++) ans=min(ans,dis[n+i*n]);
    printf("%d\n",ans);
}
int main()
{
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=m;i++)
      {
        scanf("%d%d%d",&x,&y,&z);
        AddEdge(x,y,z); AddEdge(y,x,z);
        for(int j=1;j<=k;j++)
          {
            AddEdge(x+j*n,y+j*n,z);
            AddEdge(y+j*n,x+j*n,z);
            AddEdge(x+(j-1)*n,y+j*n,z>>1);
            AddEdge(y+(j-1)*n,x+j*n,z>>1);
          }
      }
    dijkstra(1);
    return 0;
}