最大流算法的Edmonds-Karp算法,Maxflow返回最大流的值
#include<bits/stdc++.h>
using namespace std;
const int inf=2e9;
const int maxn=10050;
struct Edge{
int from,to,cap,flow;
Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f){}
};
struct Dinic{
int n,m,s,t; //结点数,边数(包括反向弧),源点编号和汇点编号
vector<Edge> edges; //边表,edges[e]和edges[e^1]互为反向弧
vector<int> g[maxn];//邻接表,g[i][j]表示结点i的第j条边在e数组中的序号
bool vis[maxn]; //BFS使用
int d[maxn]; //从起点到i的距离
int cur[maxn]; //当前弧下标
void init(int n){
this->n=n;
for(int i=0;i<n;++i) g[i].clear();
edges.clear();
}
void add(int from,int to,int cap){
edges.push_back(Edge(from,to,cap,0));
edges.push_back(Edge(to,from,0,0));
m=edges.size();
g[from].push_back(m-2);
g[to].push_back(m-1);
}
bool BFS(){
memset(vis,0,sizeof(vis));
queue<int> que;
que.push(s);
d[s]=0;
vis[s]=1;
while(!que.empty()){
int x=que.front();
que.pop();
for(int i=0;i<g[x].size();++i){
Edge& e=edges[g[x][i]];
if(!vis[e.to] && e.cap>e.flow){//只考虑残量网络中的弧
vis[e.to]=1;
d[e.to]=d[x]+1;
que.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){//从上次考虑的弧
Edge& e=edges[g[x][i]];
if(d[x]+1==d[e.to] && (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 Maxflow(int s,int t){
this->s=s;
this->t=t;
int flow=0;
while(BFS()){
memset(cur,0,sizeof(cur));
flow+=DFS(s,inf);
}
return flow;
}
};