[BJWC2012]冻结 分层图最短路

昨晚飞行路线之后，这道题就应该能一眼切了

题目当然也不难，跑一遍分层图最短路即可

Code:

#include<cstring>
#include<algorithm>
#include<queue>
#include<string>
#include<cstdio>
using namespace std;
void setIO(string a){
	freopen((a+".in").c_str(),"r",stdin);
}

const int maxn=300000+4;
const double inf=2000000000;
int n,m,s,cnt,k,t;
int head[maxn],to[maxn],nex[maxn];
double val[maxn];
void addedge(int u,int v,double c){
	nex[++cnt]=head[u], head[u]=cnt, to[cnt] = v, val[cnt] = c;
}
struct Node{
	int u;
	double dist;
	Node(int u=0,double dist = 0.0):u(u),dist(dist){}
	bool const operator<(Node v) const {
		return v.dist<dist;
	}
};
priority_queue<Node>Q;
double d[maxn];
bool done[maxn];
void dijkstra(){
	memset(done,false,sizeof(done));
	for(int i=0;i<maxn;++i) d[i]=inf;
	Q.push(Node(s,0.0)); d[s]=0.0;
    while(!Q.empty()){
    	int u=Q.top().u; Q.pop();
    	if(done[u]) continue;
    	done[u]=true;
    	for(int v=head[u];v;v=nex[v]){
    		if(d[u]+val[v]<d[to[v]]){
    			d[to[v]]=d[u]+val[v];
    			Q.push(Node(to[v],d[to[v]]));
    		}
    	}
    }
}
int main(){
	//setIO("input");
	scanf("%d%d%d",&n,&m,&k);
	s=1, t=maxn - 3;
	for(int i=1;i<=m;++i){
		int a,b,c;
		scanf("%d%d%d",&a,&b,&c);
		for(int j=0;j<=k;++j){
			addedge(a,b,(double)c);
			addedge(b,a,(double)c);
			if(j<k) addedge(a,b+n,(double)c/2);
			if(j<k) addedge(b,a+n,(double)c/2);
			a+=n, b+=n;
		}
	}
	for(int i=0;i<=k;++i) addedge(n+i*n,t,0);
	dijkstra();
    printf("%d",(int)d[t]);
    return 0;
}