poj 3469 Dual Core CPU——最小割

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
const int N=2e4+5,M=2e5+5,INF=0x3f3f3f3f;
int n,m,hd[N],cr[N],xnt=1,mxflow,dfn[N];
int num;
struct Ed{
  int nxt,to,cap;
  Ed(int n=0,int t=0,int c=0):nxt(n),to(t),cap(c) {}
}ed[(N+M)<<2];
void add(int x,int y,int z)
{
  ed[++xnt]=Ed(hd[x],y,z);hd[x]=xnt;
  ed[++xnt]=Ed(hd[y],x,0);hd[y]=xnt;
}
bool bfs()
{
  memset(dfn,0,sizeof dfn);
  dfn[0]=1;queue<int> q;q.push(0);
  while(q.size())
    {
      int k=q.front();q.pop();
      for(int i=hd[k],v;i;i=ed[i].nxt)
    if(!dfn[v=ed[i].to]&&ed[i].cap)
      {
        dfn[v]=dfn[k]+1;q.push(v);
        if(v==n+1)return true;
      }
    }
  return false;
}
int dinic(int x,int flow)
{
  if(x==n+1)return flow;//!!!
  int use=0;
  for(int &i=cr[x],v;i;i=ed[i].nxt)
    if(dfn[v=ed[i].to]==dfn[x]+1&&ed[i].cap)
      {
    int tmp=dinic(v,min(ed[i].cap,flow-use));
    if(!tmp)dfn[v]=0;
    ed[i].cap-=tmp;ed[i^1].cap+=tmp;use+=tmp;
    if(use==flow)return flow;
      }
  return use;
}
int main()
{
  scanf("%d%d",&n,&m);int x,y,z;
  for(int i=1;i<=n;i++)
    {
      scanf("%d%d",&x,&y);
      add(0,i,x);add(i,n+1,y);
    }
  for(int i=1;i<=m;i++)
    {
      scanf("%d%d%d",&x,&y,&z);
      add(x,y,z);add(y,x,z);
    }
  while(bfs())
    {
      memcpy(cr,hd,sizeof hd);
      int k=dinic(0,INF);
      mxflow+=k;
    }
  printf("%d",mxflow);
  return 0;
}