https://www.luogu.org/problemnew/show/P1345

題解：

網絡流+最小割

/* *@Author: STZG *@Language: C++ */ #include <bits/stdc++.h> #include<iostream> #include<algorithm> #include<cstdlib> #include<cstring> #include<cstdio> #include<string> #include<vector> #include<bitset> #include<queue> #include<deque> #include<stack> #include<cmath> #include<list> #include<map> #include<set> //#define DEBUG #define RI register int #define endl "\n" using namespace std; typedef long long ll; //typedef __int128 lll; const int N=200+10; const int M=100000+10; const int MOD=1e9+7; const double PI = acos(-1.0); const double EXP = 1E-8; const int INF = 0x3f3f3f3f; int t,n,m,k,p,l,r,u,v,c1,c2; int ans,cnt,flag,temp,sum; int dis[N]; char str; struct node{int u,v,c;node(){};node(int form,int to,int cap):u(form),v(to),c(cap){} }; vector<node>edge; vector<int> G[N]; void Addedge(int u,int v,int cap){edge.push_back({u,v,cap});edge.push_back({u,v,0});int sz=edge.size();G[u].push_back(sz-2);G[v].push_back(sz-1); } bool bfs(int u){memset(dis,-1,sizeof(dis));dis[u]=0;queue<int>q;q.push(u);while(!q.empty()){int u=q.front();q.pop();for(int i=0;i<G[u].size();i++){node e=edge[G[u][i]];if(dis[e.v]<0&&e.c>0){dis[e.v]=dis[u]+1;q.push(e.v);}}}return dis[c2]>0; } int dfs(int u,int flow){if(u==c2)return flow;int now;for(int i=0;i<G[u].size();i++){node e=edge[G[u][i]];if(e.c>0&&dis[u]+1==dis[e.v]&&(now=dfs(e.v,min(flow,e.c)))){edge[G[u][i]].c-=now;edge[G[u][i]^1].c+=now;return now;}}return 0; } void dinic(){while(bfs(c1+n)){int res=0;while(res=dfs(c1+n,INF)){ans+=res;}} } int main() { #ifdef DEBUGfreopen("input.in", "r", stdin);//freopen("output.out", "w", stdout); #endif//ios::sync_with_stdio(false);//cin.tie(0);//cout.tie(0);//scanf("%d",&t);//int T=0;//while(t--){scanf("%d%d%d%d",&n,&m,&c1,&c2);for(int i=1;i<=n;i++)Addedge(i,n+i,1);for(int i=1;i<=m;i++){scanf("%d%d",&u,&v);Addedge(u+n,v,INF);Addedge(v+n,u,INF);}dinic();printf("%d\n",ans);//}#ifdef DEBUGprintf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC); #endif//cout << "Hello world!" << endl;return 0; }

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總結

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