一些网络流的题目

Posted 2022-02-17 liurunky

慢慢更...

模板

---

HihoCoder上的最大流模板题：网络流二·最大流最小割定理

抄的《挑战程序设计竞赛》上的代码

#include <cstdio>
#include <cmath>
#include <vector>
#include <algorithm>
#include <queue>
#include <cstring>
using namespace std;

const int MAX=10005;
const int INF=1<<30;

struct edge

    int to,cap,rev;
    edge(int x,int y,int z)
    
        to=x,cap=y,rev=z;
    
;

int s,t;
vector<edge> v[MAX];

inline void add_edge(int x,int y,int cap)

    v[x].push_back(edge(y,cap,v[y].size()));
    v[y].push_back(edge(x,0,v[x].size()-1));


int level[MAX];
queue<int> Q;

inline void bfs()

    memset(level,-1,sizeof(level));
    level[s]=0;
    Q.push(s);
    
    while(!Q.empty())
    
        int x=Q.front();
        Q.pop();
        
        for(int i=0;i<v[x].size();i++)
        
            edge &e=v[x][i];
            if(e.cap>0 && level[e.to]<0)
            
                level[e.to]=level[x]+1;
                Q.push(e.to);
            
        
    


int iter[MAX];

inline int dfs(int x,int f)

    if(x==t)
        return f;
    for(int &i=iter[x];i<v[x].size();i++)
    
        edge &e=v[x][i];
        if(e.cap>0 && level[e.to]>level[x])
        
            int d=dfs(e.to,min(f,e.cap));
            if(d>0)
            
                e.cap-=d;
                v[e.to][e.rev].cap+=d;
                return d;
            
        
    
    return 0;


inline int max_flow()

    int flow=0;
    while(1)
    
        bfs();
        if(level[t]<0)
            break;
        
        memset(iter,0,sizeof(iter));
        
        int f=0;
        while((f=dfs(s,INF))>0)
            flow+=f;
    
    return flow;


int n,m;

int main()

//    freopen("input.txt","r",stdin);
    scanf("%d%d",&n,&m);
    s=1,t=n;
    
    for(int i=1;i<=m;i++)
    
        int x,y,cap;
        scanf("%d%d%d",&x,&y,&cap);
        add_edge(x,y,cap);
    
    
    printf("%d ",max_flow());
    
    vector<int> cut;
    for(int i=1;i<=n;i++)
        if(level[i]>=0)
            cut.push_back(i);
    
    printf("%d\n",(int)cut.size());
    for(int i=0;i<cut.size();i++)
        printf("%d ",cut[i]);
    return 0;

View Code