POJ2135 最小费用最大流

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<algorithm>
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))
#define For(i,j,k) for (i=j;i<=k;i++)

const int dmax=100100,INF=1000000000;
int begin[dmax],to[dmax],w[dmax],next[dmax],c[dmax],st[dmax];
int e,n,m,ans,q[dmax],d[dmax],f[dmax];
bool p[dmax];

void add(int x,int y,int o,int l){
	st[e]=x;
	to[e]=y;
	w[e]=l;
	c[e]=o;
	next[e]=begin[x];
	begin[x]=e;
	e++;
}
void addedge(int x,int y,int o,int l){
	add(x,y,o,l);
	add(y,x,0,-l);
}
int spfa(){
	int l=0,r=1,i,k;
	For(i,0,n) d[i]=INF;
	memset(p,0,sizeof(p));
	q[1]=0;
	d[0]=0;
	p[0]=1;
	f[0]=-1;
	while (l<r){
		k=q[++l],p[k]=0;
		for (i=begin[k];i!=-1;i=next[i]){
			if (c[i] && d[to[i]]>d[k]+w[i]){
				d[to[i]]=d[k]+w[i];
				f[to[i]]=i;
				if (!p[to[i]]){
					q[++r]=to[i];
					p[to[i]]=1;
				}
			}
		}
	}
	return d[n]!=INF;
}
void plus(){
	int i,k,min=INF;
	for (i=f[n];i!=-1;i=f[st[i]])
		min=min(c[i],min);
	for (i=f[n];i!=-1;i=f[st[i]]){
		c[i]-=min;
		c[i^1]+=min;
        ans+=min*w[i];
	}
}

int main(){
	int i,j,k,x,y,z;
	memset(begin,-1,sizeof(begin));
	scanf("%d%d",&n,&m);
	For(i,1,m){
		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++;
	while (spfa()) plus();
	printf("%d\n",ans);
	return 0;
}