【模板】网络流-最大流 Dinic
洛谷 3376
1 #include<cstdio> 2 #include<algorithm> 3 #include<cstring> 4 #define N 10010 5 #define rg register 6 using namespace std; 7 int n,m,S,T,tot,ans,last[N],d[N],q[N],cur[N]; 8 struct edge{ 9 int to,pre,f; 10 }e[200010]; 11 inline int read(){ 12 int k=0,f=1; char c=getchar(); 13 while(c<'0'||c>'9')c=='-'&&(f=-1),c=getchar(); 14 while('0'<=c&&c<='9')k=k*10+c-'0',c=getchar(); 15 return k*f; 16 } 17 bool bfs(){ 18 memset(d,-1,sizeof(d)); 19 d[S]=0; 20 int front=0,rear=1; q[front]=S; 21 while(front<rear){ 22 int now=q[front++]; 23 for(rg int i=last[now],to;i;i=e[i].pre) 24 if(d[to=e[i].to]==-1&&e[i].f) d[to]=d[now]+1,q[rear++]=to; 25 } 26 return d[T]>=0; 27 } 28 int dfs(int x,int a){ 29 if(x==T||a==0) return a; 30 int flow=0,f; 31 for(rg int &i=cur[x],to;i;i=e[i].pre) 32 if(d[to=e[i].to]==d[x]+1&&e[i].f&&(f=dfs(to,min(a,e[i].f)))){ 33 e[i].f-=f; e[i^1].f+=f; flow+=f; a-=f; 34 if(!a) break; 35 } 36 return flow; 37 } 38 int dinic(){ 39 int ans=0; 40 while(bfs()){ 41 for(rg int i=1;i<=n;i++) cur[i]=last[i]; 42 ans+=dfs(S,2e9); 43 } 44 return ans; 45 } 46 int main(){ 47 n=read(); m=read(); S=read(); T=read(); tot=1; 48 for(rg int i=1;i<=m;i++){ 49 int u=read(),v=read(); 50 e[++tot]=(edge){v,last[u],read()}; last[u]=tot; 51 e[++tot]=(edge){u,last[v],0}; last[v]=tot; 52 } 53 printf("%d\n",dinic()); 54 return 0; 55 }
