2135

/*
很明显是最小费用最大流，中间所有的路径的流都是1，费用是路径长度 
由于顶点太多，必须使用邻接表了
*/

// include file
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <ctime>

#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <bitset>
#include <strstream>

#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <set>
#include <list>
#include <functional>

using namespace std;

// typedef
typedef long long LL;
typedef unsigned long long ULL;

// 
#define read freopen("in.txt","r",stdin)
#define write freopen("out.txt","w",stdout)
#define FORi(a,b,c) for(int i=(a);i<(b);i+=c)
#define FORj(a,b,c) for(int j=(a);j<(b);j+=c)
#define FORk(a,b,c) for(int k=(a);k<(b);k+=c)
#define FORp(a,b,c) for(int p=(a);p<(b);p+=c)

#define FF(i,a)    for(int i=0;i<(a);i+++)
#define FFD(i,a)   for(int i=(a)-1;i>=0;i--)
#define Z(a) (a<<1)
#define Y(a) (a>>1)

const double eps = 1e-6;
const double INFf = 1e10;
const int INFi = 1000000000;
const double Pi = acos(-1.0);

template<class T> inline T sqr(T a){return a*a;}
template<class T> inline T TMAX(T x,T y)
{
	if(x>y) return x;
	return y;
}
template<class T> inline T TMIN(T x,T y)
{
	if(x<y) return x;
	return y;
}
template<class T> inline void SWAP(T &x,T &y)
{
	T t = x;
	x = y;
	y = t;
}
template<class T> inline T MMAX(T x,T y,T z)
{
	return TMAX(TMAX(x,y),z);
}


// code begin
#define MAXN 1010
#define MAXM 41000

struct node
{
	int s;
	int e;
	int next;
	int remain;
	int cost;
};

node mem[MAXM];
int G[MAXN];

class MinCostMaxFlow_fordfulkerson_SPFA_queue
{
private:
	int N,source,sink;
	int dx;

	// SPFA用
	int dist[MAXN];
	int isin[MAXN];
	int cnt[MAXN];
	int fat[MAXN];
	int que[MAXN]; //BFS用

	int flow;
	int cost;
public:
	MinCostMaxFlow_fordfulkerson_SPFA_queue(){}
	void Set(int Nt,int sourcet,int sinkt)
	{
		N = Nt;
		source = sourcet;
		sink = sinkt;
	}
	void Init()
	{
		dx = 0;
		memset(G,-1,sizeof(G));
	}
	void Add_edge(int a,int b,int f,int c)
	{
		mem[dx].s = a;
		mem[dx].e = b;
		mem[dx].remain = f;
		mem[dx].cost = c;
		mem[dx].next = G[a];
		G[a] = dx++;

		mem[dx].s = b;
		mem[dx].e = a;
		mem[dx].remain = 0;
		mem[dx].cost = -c;
		mem[dx].next = G[b];
		G[b] = dx++;
	}

	int Getflow(){return flow;}
	int Getcost(){return cost;}

public:
	int SPFA() // bellman ford queue optimization
	{
		// from source 
		fill(dist,dist+N+1,INFi);
		memset(isin,0,sizeof(isin));
		memset(cnt,0,sizeof(cnt));
		
		int head(0),tail(0);
		dist[source] = 0;
		que[tail] = source;
		tail = (tail+1)%MAXN;
		isin[source] = true;
		cnt[source] ++;

		while(head!=tail)
		{
			int cur = que[head];
			isin[cur] = false;
			head = (head+1)%MAXN;
			
			int mdx = G[cur];

			while(mdx!=-1)
			{
				int v = mem[mdx].e;
				if( mem[mdx].remain!=0 && dist[cur]+mem[mdx].cost<dist[v])
				{
					dist[v] = dist[cur] + mem[mdx].cost;
					fat[v] = mdx;
					if(!isin[v])
					{
						isin[v] = true;
						cnt[v] ++;
						que[tail] = v;
						tail = (tail+1)%MAXN;
					}
				}
				mdx = mem[mdx].next;
			}
		
		}

		if(dist[sink]==INFi) return -1;
		return dist[sink];
	}

	int Augment()
	{
		int minp = INFi;
		int mdx = fat[sink];
		while(mem[mdx].s!=source)
		{
			if( mem[mdx].remain<minp )
			{
				minp = mem[mdx].remain;
			}
			mdx = fat[mem[mdx].s];
		}
		
		mdx = fat[sink];
		while(mem[mdx].s!=source)
		{
			mem[mdx].remain -= minp;
			mem[mdx^1].remain += minp;
			mdx = fat[mem[mdx].s];
		}

		return minp;
	}

	void mincostmaxflow()
	{
		cost=0;
		flow=0;
		int fdx;
		int cdx;
		while((cdx=SPFA())!=-1)
		{
			fdx = Augment();
			cost += cdx*fdx;
			flow += fdx;
		}

	}
};

int N,M,source,sink;
MinCostMaxFlow_fordfulkerson_SPFA_queue g;
int main()
{
	read;
	write;
	int a,b,c;
	while(scanf("%d %d",&N,&M)!=-1)
	{
		source = N+1;
		sink = N+2;
		g.Init();
		g.Set(N+2,source,sink);

		FORi(1,M+1,1)
		{
			scanf("%d %d %d",&a,&b,&c);
			g.Add_edge(a,b,1,c);
			g.Add_edge(b,a,1,c);
		}
		g.Add_edge(source,1,2,0);
		g.Add_edge(N,sink,2,0);
		g.mincostmaxflow();
		printf("%d\n",g.Getcost());
	}
	return 0;
}

转载于:https://www.cnblogs.com/ac2012/archive/2011/03/18/1988390.html