网络流输出二分匹配方案

  1 #define IOS ios_base::sync_with_stdio(0); cin.tie(0);
  2 #include <cstdio>//sprintf islower isupper
  3 #include <cstdlib>//malloc  exit strcat itoa system("cls")
  4 #include <iostream>//pair
  5 #include <fstream>//freopen("C:\\Users\\13606\\Desktop\\草稿.txt","r",stdin);
  6 #include <bitset>
  7 //#include <map>
  8 //#include<unordered_map>
  9 #include <vector>
 10 #include <stack>
 11 #include <set>
 12 #include <string.h>//strstr substr
 13 #include <string>
 14 #include <time.h>// srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;
 15 #include <cmath>
 16 #include <deque>
 17 #include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less
 18 #include <vector>//emplace_back
 19 //#include <math.h>
 20 #include <cassert>
 21 //#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor
 22 #include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)
 23 using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation
 24 //******************
 25 int abss(int a);
 26 int lowbit(int n);
 27 int Del_bit_1(int n);
 28 int maxx(int a,int b);
 29 int minn(int a,int b);
 30 double fabss(double a);
 31 void swapp(int &a,int &b);
 32 clock_t __STRAT,__END;
 33 double __TOTALTIME;
 34 void _MS(){__STRAT=clock();}
 35 void _ME(){__END=clock();__TOTALTIME=(double)(__END-__STRAT)/CLOCKS_PER_SEC;cout<<"Time: "<<__TOTALTIME<<" s"<<endl;}
 36 //***********************
 37 #define rint register int
 38 #define fo(a,b,c) for(rint a=b;a<=c;++a)
 39 #define fr(a,b,c) for(rint a=b;a>=c;--a)
 40 #define mem(a,b) memset(a,b,sizeof(a))
 41 #define pr printf
 42 #define sc scanf
 43 #define ls rt<<1
 44 #define rs rt<<1|1
 45 typedef vector<int> VI;
 46 typedef long long ll;
 47 const double E=2.718281828;
 48 const double PI=acos(-1.0);
 49 //const ll INF=(1LL<<60);
 50 const int inf=(1<<30);
 51 const double ESP=1e-9;
 52 const int mod=(int)1e9+7;
 53 const int N=(int)2e5+10;
 54 
 55 class DINIC
 56 {
 57 public:
 58 //    const int MAXN=10004,MAXWAY=100005;
 59     int n,way,max_flow,deep[N];
 60     int tot,head[N],cur[N];
 61     struct EDGE{
 62         int to,next;
 63         int dis;
 64     }edge[N];
 65     void Init(int n)
 66     {
 67         tot=-1;//因为加反向边要^1,所以要从0开始;
 68         this->n=n;
 69         for(int i=0;i<=n;++i)
 70             head[i]=-1;
 71     }
 72     void add(int from,int to,int V,bool flag)
 73     {
 74         ++tot;
 75         edge[tot].to=to;
 76         edge[tot].dis=0;
 77         if(flag)edge[tot].dis=V;
 78         edge[tot].next=head[from];
 79         head[from]=tot;
 80     }
 81     queue<int>q;
 82     bool bfs(int s,int t)
 83     {
 84         for(int i=1;i<=n;++i)
 85             deep[i]=inf;
 86         while(!q.empty())q.pop();
 87         for(int i=1;i<=n;++i)cur[i]=head[i];
 88         deep[s]=0;
 89         q.push(s);
 90 
 91         while(!q.empty())
 92         {
 93             int now=q.front();q.pop();
 94             for(int i=head[now];i!=-1;i=edge[i].next)
 95             {
 96                 if(deep[edge[i].to]==inf&&edge[i].dis)
 97                 {
 98                     deep[edge[i].to]=deep[now]+1;
 99                     q.push(edge[i].to);
100                 }
101             }
102         }
103         return deep[t]<inf;
104     }
105     int dfs(int now,int t,int limit)
106     {
107         if(!limit||now==t)return limit;
108         int flow=0,f;
109         for(int i=cur[now];i!=-1;i=edge[i].next)
110         {
111             cur[now]=i;
112             if(deep[edge[i].to]==deep[now]+1&&(f=dfs(edge[i].to,t,min(limit,edge[i].dis))))
113             {
114                 flow+=f;
115                 limit-=f;
116                 edge[i].dis-=f;
117                 edge[i^1].dis+=f;
118                 if(!limit)break;
119             }
120         }
121         return flow;
122     }
123     void Dinic(int s,int t)
124     {
125         while(bfs(s,t))
126             max_flow+=dfs(s,t,inf);
127     }
128 }G;
129 
130 int main()
131 {
132     int m,n;
133     sc("%d%d",&m,&n);
134     int u,v,cnt=0;
135     G.Init(n+2);
136     while(sc("%d%d",&u,&v),u!=-1&&v!=-1)
137     {
138         u++,v++;
139         cnt++;
140         G.add(u,v,1,1);G.add(v,u,1,0);
141     }
142     cnt*=3;
143     for(int i=2;i<=m+1;++i)
144     {
145         G.add(1,i,1,1);
146         G.add(i,1,1,0);
147     }
148     for(int i=m+2;i<=n+1;++i)
149     {
150         G.add(i,n+2,1,1);
151         G.add(n+2,i,1,0);
152     }
153     G.Dinic(1,n+2);
154     pr("%d\n",G.max_flow);
155     for(int i=1,j=0;i<=cnt;++i,j+=2)
156     {
157         if(G.edge[j].to!=1&&G.edge[j+1].to!=1)
158             if(G.edge[j].to!=n+2&&G.edge[j+1].to!=n+2)
159                 if(G.edge[j+1].dis)//网络流可以判断正向边是否有流量（即反向边的残量是否不为 0）
160                 {
161                     pr("%d %d\n",G.edge[j+1].to-1,G.edge[j].to-1);
162                 }
163     }
164     return 0;
165 }
166 
167 /**************************************************************************************/
168 
169 int maxx(int a,int b)
170 {
171     return a>b?a:b;
172 }
173 
174 void swapp(int &a,int &b)
175 {
176     a^=b^=a^=b;
177 }
178 
179 int lowbit(int n)
180 {
181     return n&(-n);
182 }
183 
184 int Del_bit_1(int n)
185 {
186     return n&(n-1);
187 }
188 
189 int abss(int a)
190 {
191     return a>0?a:-a;
192 }
193 
194 double fabss(double a)
195 {
196     return a>0?a:-a;
197 }
198 
199 int minn(int a,int b)
200 {
201     return a<b?a:b;
202 }