最小费用最大流算法

poj 2135 最小费用最大流模板题目；

#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<climits>
#include<cctype>
#include<iostream>
#include<algorithm>
#include<queue>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<string>
#define ll long long
#define MAX 1010
#define eps 1e-8
#define INF INT_MAX

using namespace std;

struct Edge{
	int from, to,cap,flow,cost;
};

vector<int>G[MAX];
vector<Edge>edges;

int n;

void init(){
	for (int i=0; i<MAX; i++)G[i].clear();
	edges.clear();
}

void addEdge(int from, int to, int cap, int cost){
	edges.push_back((Edge){from,to,cap,0,cost});
	edges.push_back((Edge){to,from,0,0,-cost});
	int k = edges.size();
	G[from].push_back(k-2);
	G[to].push_back(k-1);
}

int d[MAX],inq[MAX],p[MAX],a[MAX];

bool Bellman_ford(int s, int t, int& flow, int& cost){
	for (int i=0; i<n; i++) d[i] = (i == s ? 0 : INF);
	memset(inq,0,sizeof(inq));
	queue<int>q;
	inq[s] = 1;
	p[s] = 0;
	a[s] = INF;
	q.push(s);
	while (!q.empty()){
		int u = q.front();
		q.pop();
		inq[u] = 0;
		for (int i=0; i<G[u].size(); i++){
			Edge& e = edges[G[u][i]];
			if (e.cap > e.flow && d[e.to] > d[u] + e.cost){
				d[e.to] = d[u] + e.cost;
				p[e.to] = G[u][i];
				a[e.to] = min(a[u],e.cap - e.flow);
				if (!inq[e.to]){
					q.push(e.to);
					inq[e.to] = 1;		
				}
			}
		}
	}
	if (d[t] == INF) return false;
	flow += a[t];
	cost += a[t]*d[t];
	int u = t;
	while (u != s){
		edges[p[u]].flow += a[t];
		edges[p[u]^1].flow -= a[t];
		u = edges[p[u]].from;
	}
	return true;
}

int Mincost(int s, int t){
	int flow = 0,cost = 0;
	while (Bellman_ford(s,t,flow,cost));
	return cost;
}

int main(){
	int m;
	while (scanf("%d%d",&n,&m) != EOF){
		int x,y,z;
		init();
		for (int i=0; i<m; i++){
			scanf("%d%d%d",&x,&y,&z);
			addEdge(x,y,1,z);
			addEdge(y,x,1,z);
		}
		addEdge(0,1,2,0);
		addEdge(n,n+1,2,0);
		n += 2;
		printf("%d\n",Mincost(0,n-1));
	}
	return 0;
}