bzoj 2662 [BeiJing wc2012]冻结——分层图

题目：https://www.lydsy.com/JudgeOnline/problem.php?id=2662

这种的都是分层图。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int N=55,M=1005;
int n,m,K,hd[N],xnt,dis[N][N],ans=0x3f3f3f3f;
bool vis[N][N];
struct Ed{
    int nxt,to,w;
    Ed(int n=0,int t=0,int w=0):nxt(n),to(t),w(w) {}
}ed[M<<1];
struct Node{
    int c,a,b;
    Node(int c=0,int a=0,int b=0):c(c),a(a),b(b) {}
    bool operator< (const Node &b)const
    {return c>b.c;}
};
void add(int x,int y,int z)
{
    ed[++xnt]=Ed(hd[x],y,z);hd[x]=xnt;
    ed[++xnt]=Ed(hd[y],x,z);hd[y]=xnt;
}
priority_queue<Node> q;
void dj()
{
    memset(dis,0x3f,sizeof dis);
    dis[1][0]=0;
    q.push(Node(0,1,0));
    while(q.size())
    {
        int a=q.top().a,b=q.top().b;q.pop();
        while(q.size()&&vis[a][b])a=q.top().a,b=q.top().b,q.pop();
        if(vis[a][b])break;vis[a][b]=1;
        for(int i=hd[a],v;i;i=ed[i].nxt)
        {
            if(dis[v=ed[i].to][b]>dis[a][b]+ed[i].w)
                dis[v][b]=dis[a][b]+ed[i].w,q.push(Node(dis[v][b],v,b));
            if(b<K&&dis[v][b+1]>dis[a][b]+(ed[i].w>>1))
                dis[v][b+1]=dis[a][b]+(ed[i].w>>1),q.push(Node(dis[v][b+1],v,b+1));
        }
    }
}
int main()
{
    scanf("%d%d%d",&n,&m,&K);
    int x,y,z;
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d%d",&x,&y,&z);
        add(x,y,z);
    }
    dj();
    for(int i=0;i<=K;i++)ans=min(ans,dis[n][i]);
    printf("%d\n",ans);
    return 0;
}