luogo_3376 网络最大流

#include<bits/stdc++.h>

using namespace std;

#define MAXN 100010

#define INF 100000000

struct Edge{int from,to,cap,flow;};

vector<Edge> edges;

vector<int> G[MAXN];

int n,m,s,t,cur[MAXN],d[MAXN],u,v,w;

bool vis[MAXN];

void addedge(int from,int to,int cap){

edges.push_back((Edge){from,to,cap,0});

edges.push_back((Edge){to,from,0,0});

int x=edges.size();

G[from].push_back(x-2);

G[to].push_back(x-1);

}

bool bfs(){

memset(vis,0,sizeof(vis));

queue<int> Q;

Q.push(s); vis[s]=1; d[s]=0;

while(!Q.empty()){

int x=Q.front(); Q.pop();

for(int i=0;i<G[x].size();i++){

Edge& e=edges[G[x][i]];

if(!vis[e.to] && e.cap>e.flow){

vis[e.to]=1;

d[e.to]=d[x]+1;

Q.push(e.to);

}

}

}

return vis[t];

}

int dfs(int x,int a){

if(x==t || a==0)return a;

int flow=0,f;

for(int& i=cur[x];i<G[x].size();i++){

Edge& e=edges[G[x][i]];

if(d[e.to]==d[x]+1 && (f=dfs(e.to,min(a,e.cap-e.flow)))>0){

e.flow+=f;

edges[G[x][i]^1].flow-=f;

flow+=f;

a-=f;

if(a==0)break;

}

}

return flow;

}

int Dinic(){

int flow=0;

while(bfs()){

memset(cur,0,sizeof(cur));

flow+=dfs(s,INF);

}

return flow;

}

int main(){

scanf("%d%d%d%d",&n,&m,&s,&t);

for(int i=1;i<=m;i++){

scanf("%d%d%d",&u,&v,&w);

addedge(u,v,w);

}

cout<<Dinic()<<endl;

return 0;

}