洛谷 P2939 [USACO09FEB]改造路Revamping Trails

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=3e6;
int read()
{
	int sum=0;char ch=getchar();
	while(ch<'0'||ch>'9') ch=getchar();
	while(ch<='9'&&ch>='0')
	{
		sum=sum*10+ch-'0';
		ch=getchar();
	}
	return sum;
}
int n,m,k,dis[2*maxn],cnt,v[maxn];
int head[2*maxn],nxt[2*maxn],to[2*maxn],w[2*maxn];
void add(int x,int y,int z)
{
	cnt++;nxt[cnt]=head[x];head[x]=cnt;to[cnt]=y;w[cnt]=z;
}
priority_queue<pair<int ,int > >q;
void dijstra()
{
	memset(dis,0x3f,sizeof(dis));
	memset(v,0,sizeof(v));
	dis[1]=0;q.push(make_pair(0,1));
	while(!q.empty())
	{
		int x=q.top().second;q.pop();
		if(v[x]) continue; v[x]=1;
		for(int i=head[x];i;i=nxt[i])
		{
			int y=to[i],z=w[i];
			if(dis[y]>dis[x]+z)
			{
				dis[y]=dis[x]+z;
				q.push(make_pair(-dis[y],y));
			}
		}
	}
}
int main()
{
	n=read();m=read();k=read();
	for(int x,y,z,i=1;i<=m;i++)
	{
		x=read();y=read();z=read();
		for(int j=0;j<=k;j++)
		{
			add(x+j*n,y+j*n,z);
			add(y+j*n,x+j*n,z);
			if(j!=k)
			{
				add(x+j*n,y+(j+1)*n,0);
				add(y+j*n,x+(j+1)*n,0);
			}
		}
	}
	dijstra();
	int ans=2147483640;
	for(int i=0;i<=k;i++)
		ans=min(ans,dis[n+i*n]);
	cout<<ans;
	return 0;
}