BZOJ P2662 [BeiJing wc2012]冻结【分层图最短路】

分层建图跑最短路

#include <queue>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define rep(i,x,y) for(int i=(x);i<=(y);i++)
#define repl(i,x,y) for(int i=(x);i<(y);i++)
#define repd(i,x,y) for(int i=(x);i>=(y);i--)
using namespace std;

const int N=1e6+5;
const int Inf=1e18;

int n,m,t,ans=Inf,dis[N],vis[N];
int cnt,to[N<<1],nxt[N<<1],edge[N<<1],head[N];

char buf[1<<20],*p1,*p2;
#define gc (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<20,stdin),p1==p2)?0:*p1++)
inline int read() {
    int x=0;char ch=gc;bool f=0;
    while(ch>'9'||ch<'0'){if(ch=='-')f=1;ch=gc;}
    while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=gc;}
    return f?-x:x;
}

void ins(int x,int y,int z) {
	to[++cnt]=y;edge[cnt]=z;nxt[cnt]=head[x];head[x]=cnt;
}

void spfa(int s) {
	queue<int>q;
	rep(i,1,n*(t+1)) dis[i]=Inf;
	q.push(s);vis[s]=1;dis[s]=0;
	while(q.size()) {
		int x=q.front();q.pop();
		vis[x]=0;
		for(int i=head[x];i;i=nxt[i]) {
			int y=to[i],z=edge[i];
			if(dis[x]+z<dis[y]) {
				dis[y]=dis[x]+z;
				if(!vis[y]) {
					vis[y]=1;q.push(y);
				}
			}
		}
	}
}

int main() {
	n=read(),m=read(),t=read();
	
	rep(i,1,m) {
		int x=read(),y=read(),z=read();
		rep(j,0,t-1) {
			ins(x+j*n,y+j*n,z);ins(y+j*n,x+j*n,z);
			ins(x+j*n,y+(j+1)*n,z>>1);ins(y+j*n,x+(j+1)*n,z>>1);
		}
		ins(x+n*t,y+n*t,z);ins(y+n*t,x+n*t,z);
	}

	spfa(1);
	
	rep(i,0,t) ans=min(ans,dis[(i+1)*n]);
	
	printf("%d",ans);

	return 0;
}