传送门：https://www.luogu.org/problem/P3386
已经加入极其简单的当前弧优化
1 #include<bits/stdc++.h>
2 using namespace std;
3 int n,m,bian,s,t;
4 int vis;
5 int dep[6000001];
6 int inque[6000001];
7 int cur[6000001];
8 int maxflow=0;
9 struct edge{
10 int to,nxt,flow;
11 }e[6000001];int tot=-1;
12 int first[6000001];
13 const int inf=0x3f3f3f3f;
14 inline int kd()
15 {
16 int x=0,f=1;char ch=getchar();
17 while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
18 while(ch>='0'&&ch<='9'){x=x*10+(ch^48);ch=getchar();}
19 return x*f;
20 }
21 inline void add_edge(int a,int b,int c)
22 {
23 e[++tot].to=b;
24 e[tot].flow=c;
25 e[tot].nxt=first[a];
26 first[a]=tot;
27 }
28 bool bfs()
29 {
30 for(register int i=0;i<=n+m+2;i++)cur[i]=first[i],inque[i]=false,dep[i]=0x3f3f3f3f;
31 dep[s]=0;
32 queue<int>q;
33 q.push(s);
34 while(q.empty()==false)
35 {
36 int now=q.front();
37 q.pop();
38 inque[now]=false;
39 for(int i=first[now];i!=-1;i=e[i].nxt)
40 {
41 int to=e[i].to;
42 if(dep[now]+1<dep[to]&&e[i].flow!=0)
43 {
44 dep[to]=dep[now]+1;
45 if(inque[to]==false)
46 {
47 inque[to]=true;
48 q.push(to);
49 }
50 }
51 }
52 }
53 if(dep[t]==0x3f3f3f3f)return false;
54 return true;
55 }
56 int dfsl(int now,int nowflow)
57 {
58 int rlow=0;
59 if(now==t)
60 {
61 vis=1;
62 maxflow+=nowflow;
63 return nowflow;
64 }
65 int used=0;
66 for(int i=cur[now];i!=-1;i=e[i].nxt)
67 {
68 cur[now]=i;
69 if(dep[now]+1==dep[e[i].to]&&e[i].flow!=0)
70 {
71 if(rlow=dfsl(e[i].to,min(nowflow,e[i].flow)))
72 {
73 used+=rlow;
74 e[i].flow-=rlow;
75 e[i^1].flow+=rlow;
76 if(used==nowflow)return nowflow;
77 }
78 }
79 }
80 if(used==0)dep[now]=0x3f3f3f3f;
81 return used;
82 }
83 void dinic()
84 {
85 while(bfs())
86 {
87 vis=1;
88 while(vis==1)
89 {
90 vis=0;
91 dfsl(s,inf);
92 }
93 }
94 return;
95 }
96 int main()
97 {
98 memset(first,-1,sizeof(first));
99 n=kd(),m=kd(),bian=kd(),s=1,t=m+n+2;
100 for(int i=1;i<=n;i++)
101 {
102 add_edge(1,i+1,1);
103 add_edge(i+1,1,0);
104 }
105 for(int i=1;i<=bian;i++)
106 {
107 int a=kd(),b=kd();
108 if(a>n||b>m)continue;
109 add_edge(a+1,b+n+1,1);
110 add_edge(b+n+1,a+1,0);
111 }
112 for(int i=1;i<=m;i++)
113 {
114 add_edge(i+n+1,n+m+2,1);
115 add_edge(n+m+2,i+n+1,0);
116 }
117 dinic();
118 cout<<maxflow<<endl;
119 }