poj 3041 网络流做法 sap+gap

#include<iostream>#include<algorithm>#include<cstring>#include<cstdio>#define min(a,b) (a)>(b)?(b):(a)#define max(a,b) (a)>(b)?(a):(b)#define inf 99999999using namespace std;int cnt;int source,N;int sink,ans;int c[4400];int H[20410];int d[4410];struct egde{    int u,v,c,next;};egde a[20000];void init(){    int i;    for(i=0;i<24000;i++)        H[i]=-1;    cnt=0;}void add(int u,int v,int c){    a[cnt].v=v;    a[cnt].c=c;    a[cnt].next=H[u];    H[u]=cnt++;}void build(int u,int v,int c){    add(u,v,c);    add(v,u,0);}int dfs(int u,int flow){      if(u==sink)        return flow;    int tt,res=0,delta;    for(tt=H[u];~tt;tt=a[tt].next)    {        int &v=a[tt].v,&c=a[tt].c;        if(c&&d[u]==d[v]+1){        delta=dfs(v,min(flow,c));        c-=delta;        a[tt^1].c+=delta;        res+=delta;        flow-=delta;        if (!flow)             return res;        }    }    if(!res)    {        if(!--c[d[u]])             d[source]=N+1;        ++c[++d[u]];    }    return res;}void sap(){    memset(c,0,sizeof(c));     memset(d,0,sizeof(d));    c[source]=N;    while(d[source]<N)        ans+=dfs(source,inf);}int main(){int n,k,i,x,y;while(~scanf("%d%d",&n,&k)){init();source=0;sink=n*2+1;N=sink+1;ans=0;for(i=1;i<=k;i++){scanf("%d%d",&x,&y);build(x,y+n,inf);}for(i=1;i<=n;i++){build(source,i,1);build(i+n,sink,1);}sap();printf("%d\n",ans);}return 0;}