POJ 2135 Farm Tour （最小费用最大流）

POJ 2135 Farm Tour  （最小费用最大流）

两遍spfa解决

#include <iostream>
#include <cstdio>
#include <queue>
#include <cstdlib>
#include <algorithm>
using namespace std;

const int maxn=30000;
const int inf=2000000000;
struct edge{
	int u,v,next,f,c;
	edge(int u0=0,int v0=0,int f0=0,int c0=0,int next0=0){
		u=u0,v=v0,f=f0,c=c0,next=next0;
	}	
}e[maxn*10];
int head[maxn*2],visited[maxn*2],path[maxn*2],dist[maxn*2];
int cnt,from,to,marked,n,r,m;

void initial(){
	cnt=0;marked=1;
	from=1;to=n;
	for(int i=0;i<=n;i++){
		head[i]=-1;
		visited[i]=0;
	}
}

void adde(int u,int v,int f,int c){
	e[cnt].u=u,e[cnt].v=v,e[cnt].f=f,e[cnt].c=c,e[cnt].next=head[u],head[u]=cnt++;
	e[cnt].u=v,e[cnt].v=u,e[cnt].f=0,e[cnt].c=-c,e[cnt].next=head[v],head[v]=cnt++;
}

void input(){
	int u0,v0,c0;
	while(m-- >0){
		scanf("%d%d%d",&u0,&v0,&c0);
		adde(u0,v0,1,c0);
		adde(v0,u0,1,c0);
	}
}

void bfs(){
	 for(int i=0;i<=n;i++){
	 	dist[i]=inf;
	 	path[i]=-1;
	 }
	 dist[from]=0;
     queue <int> q;
     q.push(from);
     marked++;
     visited[from]=marked;
     while(!q.empty()){
         int s=q.front();
         q.pop();
         for(int i=head[s];i!=-1;i=e[i].next){
              int d=e[i].v;
              if(e[i].f>0 && dist[s]+e[i].c<dist[d]){
                 dist[d]=dist[s]+e[i].c;
                 path[d]=i;
                 if(visited[d]!=marked){
                 	visited[d]=marked;
                 	q.push(d);
                 }
              }
         }
         visited[s]=-1;
     }
}

void computing(){
	int k=2,ans=0;
	while(k-- >0){
    	bfs();
		ans+=dist[to];
		for(int i=to;i!=from;i=e[path[i]].u){
     		e[path[i]].f-=1;
        	e[path[i]^1].f+=1;
    	}
    }
	cout<<ans<<endl;
}

int main(){
	while(scanf("%d%d",&n,&m)!=EOF){
		initial();
		input();
		computing();
	}
	return 0;
}