思路：裸的分层图最短路
提交：1次
题解：
如思路
代码：
#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#define R register int
using namespace std;
#define ull unsigned long long
#define ll long long
#define pause (for(R i=1;i<=10000000000;++i))
#define IN freopen("NOIPAK++.in","r",stdin)
#define OUT freopen("out.out","w",stdout)
namespace Fread {
static char B[1<<15],*S=B,*D=B;
#ifndef JACK
#define getchar() (S==D&&(D=(S=B)+fread(B,1,1<<15,stdin),S==D)?EOF:*S++)
#endif
inline int g() {
R ret=0,fix=1; register char ch; while(!isdigit(ch=getchar())) fix=ch=='-'?-1:fix;
if(ch==EOF) return EOF; do ret=ret*10+(ch^48); while(isdigit(ch=getchar())); return ret*fix;
} inline bool isempty(const char& ch) {return ch!=EOF&&(ch<=36||ch>=127);}
inline void gs(char* s) {
register char ch; while(isempty(ch=getchar())); if(ch==EOF) return ;
do *s++=ch; while(!isempty(ch=getchar()));
}
}using Fread::g; using Fread::gs;
const int N=10010,M=50010;
#define fr first
#define sc second
#define mp make_pair
#define pii pair<int,int>
int n,m,k,s,t,cnt,ans=0x3f3f3f3f;
int vr[M<<1],nxt[M<<1],fir[N],w[M<<1],d[N][15]; bool vis[N][15];
inline void add(int u,int v,int ww) {vr[++cnt]=v,nxt[cnt]=fir[u],w[cnt]=ww,fir[u]=cnt; }
inline void dijk() { priority_queue<pair<int,pii > > q;
memset(d,0x3f,sizeof(d)); d[s][0]=0; q.push(mp(0,mp(s,0)));
while(q.size()) { register pii tmp=q.top().sc; q.pop();
R u=tmp.fr,t=tmp.sc; if(vis[u][t]) continue;
for(R i=fir[u];i;i=nxt[i]) { R v=vr[i];
if(d[v][t]>d[u][t]+w[i]) d[v][t]=d[u][t]+w[i],q.push(mp(-d[v][t],mp(v,t)));
if(t<k&&d[v][t+1]>d[u][t]) d[v][t+1]=d[u][t],q.push(mp(-d[v][t+1],mp(v,t+1)));
}
}
}
signed main() {
#ifdef JACK
#endif
n=g(),m=g(),k=g(),s=g(),t=g(); for(R i=1,u,v,w;i<=m;++i) u=g(),v=g(),w=g(),add(u,v,w),add(v,u,w);
dijk(); for(R i=0;i<=k;++i) ans=min(ans,d[t][i]); printf("%d
",ans);
}
2019.07.22