BZOJ 1579 [Usaco2009 Feb]Revamping Trails 道路升级

//Twenty
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<queue>
#include<vector>
typedef long long LL;
using namespace std;
const int maxn=10000+299;
const int maxm=50000*2+299;
int n,m,k,fir[maxn],nxt[maxm],to[maxm],vis[maxn][25],dis[maxn][25],ecnt;
LL val[maxm],ans;
struct node {
    int id,k;
    LL d;
    friend bool operator <(const node &A,const node &B) {
        return A.d>B.d;
    }
    node(){}
    node(int id,LL d,int k):id(id),d(d),k(k){}
};
priority_queue<node>que;
void add(int u,int v,int w) {
    nxt[++ecnt]=fir[u]; fir[u]=ecnt; to[ecnt]=v; val[ecnt]=w;
    nxt[++ecnt]=fir[v]; fir[v]=ecnt; to[ecnt]=u; val[ecnt]=w;
}
void dijkstra() {
    memset(dis,127,sizeof(dis));
    dis[1][0]=0;
    que.push(node(1,0,0));
    while(!que.empty()) {
        node x=que.top();
        vis[x.id][x.k]=1;
        que.pop();
        if(x.id==n) {ans=x.d; break;}
        for(int i=fir[x.id];i;i=nxt[i]) {
            if(!vis[to[i]][x.k]&&x.d+val[i]<dis[to[i]][x.k]) {
                dis[to[i]][x.k]=x.d+val[i];
                que.push(node(to[i],x.d+val[i],x.k)); 
            }
            if(x.k+1<=k&&!vis[to[i]][x.k+1]&&x.d<dis[to[i]][x.k+1]) {
                dis[to[i]][x.k+1]=x.d;
                que.push(node(to[i],x.d,x.k+1)); 
            }
        }
     }
}
int main()
{
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=m;i++) {
        int x,y; LL z;
        scanf("%d%d%lld",&x,&y,&z);
        add(x,y,z);
    }
    dijkstra();
    printf("%lld\n",ans);
    return 0;
}