poj Drainage Ditches（最大流入门）

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<algorithm>
#include<vector>
#define MAX 205
#define INF 0x3f3f3f3f
#define pb push_back
using namespace std;
struct edge{
int to,cap,rev;
edge(){}
edge(int to,int cap,int rev):to(to),cap(cap),rev(rev){}
};
vector<edge>G[MAX];
bool used[MAX];
void add_edge(int from,int to,int cap)
{
    G[from].pb(edge(to,cap,G[to].size()));
    G[to].pb(edge(from,0,G[from].size()-1));
}
int dfs(int v,int t,int f)
{
    if(v==t)return f;
    used[v]=true;
    for(int i=0;i<G[v].size();i++)
    {
        edge &e=G[v][i];
        //cout<<e.to<<endl;
        if(!used[e.to]&&e.cap>0)
        {
            int d=dfs(e.to,t,min(f,e.cap));
            if(d>0)
            {
                e.cap-=d;
                G[e.to][e.rev].cap+=d;
                return d;
            }
        }
    }
    return 0;
}
int max_flow(int s,int t)
{
    int flow=0;
    for(;;)
    {
        memset(used,0,sizeof(used));
        int f=dfs(s,t,INF);
        if(f==0)
            return flow;
        flow+=f;
    }
}
int main()
{
    int n,m;
       while(cin>>n>>m){
           for(int i=0;i<n;i++)
            G[i].clear();
        for(int i=0;i<n;i++)
        {
            int u,v,cap;
            cin>>u>>v>>cap;
            add_edge(u,v,cap);
        }
        cout<<max_flow(1,m)<<endl;
    }
}

#include<string.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
using namespace std;
const int maxn = 205;
const int INF = 0x3f3f3f3f;

struct Edge
{
    int from,to,cap,flow;
    Edge(){}
    Edge(int from,int to,int cap,int flow):from(from),to(to),cap(cap),flow(flow){}
};

struct Dinic
{
    int n,m,s,t;            //结点数,边数(包括反向弧),源点与汇点编号
    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,标记一个节点是否被遍历过
    int d[maxn];            //d[i]表从起点s到i点的距离(层次)
    int cur[maxn];          //cur[i]表当前正访问i节点的第cur[i]条弧

    void init(int n,int s,int t)
    {
        this->n=n,this->s=s,this->t=t;
        for(int i=0;i<=n;i++) G[i].clear();
        edges.clear();
    }

    void AddEdge(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> Q;//用来保存节点编号的
        Q.push(s);
        d[s]=0;
        vis[s]=true;
        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]=true;
                    d[e.to] = d[x]+1;
                    Q.push(e.to);
                }
            }
        }
        return vis[t];
    }

    //a表示从s到x目前为止所有弧的最小残量
    //flow表示从x到t的最小残量
    int DFS(int x,int a)
    {
        if(x==t || a==0)return a;
        int flow=0,f;//flow用来记录从x到t的最小残量
        for(int& i=cur[x]; i<G[x].size(); i++)
        {
            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;
            }
        }
        if(!flow) d[x] = -1;///炸点优化
        return flow;
    }

    int Maxflow()
    {
        int flow=0;
        while(BFS())
        {
            memset(cur,0,sizeof(cur));
            flow += DFS(s,INF);
        }
        return flow;
    }
}Di;
int main()
{
    int n,m;

    while(cin>>n>>m){
        Di.init(n,1,m);
    for(int i=0;i<n;i++)
    {
        int v,u,rap;
        cin>>u>>v>>rap;
        Di.AddEdge(u,v,rap);
    }
     cout<<Di.Maxflow()<<endl;
   }
}