hihocode#1378 : 网络流二·最大流最小割定理(最大流求最小割集)

代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>
using namespace std;
typedef long long ll;
const double PI = acos(-1.0);
const double eps = 1e-6;
const int INF = 1000000000;
const int maxn = 123456;
int T,n,m;
int tot,s,t;
int head[maxn],vis[maxn],path[maxn];
set<int>st;

struct EDGE
{
int from,to;
int cap,flow;
int next;
}e[maxn];

void init()
{
tot=0;
s=1;
t=n;
memset(head,-1,sizeof(head));
memset(vis,0,sizeof(vis));
memset(path,0,sizeof(path));
}

void add_edge(int u,int v,int w)
{
e[tot].from=u;
e[tot].to=v;
e[tot].cap=w;
e[tot].flow=0;
e[tot].next=head[u];
head[u]=tot++;
}

int bfs()
{
queue<int>q;
q.push(s);
vis[s]=1;
path[s]=-1;
while(!q.empty())
{
int u=q.front();
q.pop();
for(int i=head[u];i!=-1;i=e[i].next)
{
int v=e[i].to;
if(e[i].cap-e[i].flow>0&&!vis[v])
{
path[v]=i;
vis[v]=1;
if(v==t)
return 1;
q.push(v);
}
}
}
return 0;
}

int EK()
{
int maxFlow=0;
int flow,i;
while(bfs())
{
memset(vis,0,sizeof(vis));
i=path[t];
flow=INF;
while(i!=-1)
{
flow=min(flow,e[i].cap-e[i].flow);
i=path[e[i].from];
}
i=path[t];
while(i!=-1)
{
e[i].flow+=flow;
e[i^1].flow-=flow;
i=path[e[i].from];
}
maxFlow+=flow;
}
return maxFlow;
}

void Get_set()//求割集
{
memset(vis,0,sizeof(vis));
queue<int>q;
q.push(1);
vis[1]=1;
while(!q.empty())
{
int u=q.front();
q.pop();
st.insert(u);
for(int i=head[u];i!=-1;i=e[i].next)
{
int v=e[i].to;
if(vis[v]==0&&e[i].cap-e[i].flow>0)
{
vis[v]=1;
q.push(v);
}
}
}
}

int main()
{
while(scanf("%d%d",&n,&m)!=EOF)
{
init();
for(int i=0;i<m;i++)
{
int u,v,c;
scanf("%d%d%d",&u,&v,&c);
add_edge(u,v,c);
add_edge(v,u,0);
}
int maxFlow=EK();
Get_set();
printf("%d %d\n",maxFlow,st.size());
for(set<int>::iterator it = st.begin();it!=st.end();it++)
{
if(it!=st.begin())
printf(" ");
printf("%d",*it);
}
printf("\n");
}
return 0;
}