UVALive 3645 Objective: Berlin（最大流）

题目地址：https://icpcarchive.ecs.baylor.edu/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1646

思路：拆点，将航线看做点。设一源点与汇点。对于每个航线i，将其拆为两点，i和i'，连一条容量为最大客容量的边；对于所有起点为出发点的航线j，连一条源点到j的容量为INF的边；对于所有终点为目标点的航线k，连一条k到汇点的容量为INF的边；对于可换乘的航线i、j，连一条i-->j'容量为INF的边。求从源点到汇点的最大流即可。注意换乘时在同一地点。

#include<map>
#include<queue>
#include<cstdio>
#include<vector>
#include<cstring>
#include<iostream>
#include<algorithm>
#define debu
using namespace std;
const int maxn=10000+10;
const int maxm=5000+50;
const int INF=0x3f3f3f3f;
struct Edge
{
    int from,to,cap,flow;
    Edge(int a=0,int b=0,int c=0,int d=0):from(a),to(b),cap(c),flow(d) {}
};
struct Node
{
    string x,y;
    int Tst,Ted,c;
};
struct Dinic
{
    int n,m,s,t;
    vector<Edge> edges;
    vector<int> G[maxn];
    bool vis[maxn];
    int d[maxn];
    int cur[maxn];
    void init(int n)
    {
        this->n=n;
        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));
        int 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;
        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[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;
    }
};
Dinic g;
Node a[maxm];
int tot,n,ENDT,m;
int main()
{
#ifdef debug
    freopen("in.in","r",stdin);
#endif // debug
    ios::sync_with_stdio(0);
    while(cin>>n)
    {
        string st,ed;
        cin>>st>>ed>>ENDT>>m;
        g.init(2*m+1);
        for(int i=1; i<=m; i++)
        {
            cin>>a[i].x>>a[i].y>>a[i].c>>a[i].Tst>>a[i].Ted;
            if(a[i].x==st) g.addedge(0,i,INF);
            if(a[i].y==ed&&a[i].Ted<=ENDT) g.addedge(i+m,2*m+1,INF);
            g.addedge(i,i+m,a[i].c);
        }
        for(int i=1; i<=m; i++)
        {
            if(a[i].Ted>=ENDT) continue;
            for(int j=1; j<=m; j++)
            {
                if(i==j) continue;
                int tmp1=(a[i].Ted%100);
                int tmp2=(a[i].Ted/100);
                tmp2+=(tmp1+30>=60)?1:0;
                tmp1=(tmp1+30)%60;
                if(tmp1+tmp2*100<=a[j].Tst&&a[j].Ted<=ENDT)
                {
                    if(a[i].y==a[j].x) g.addedge(i+m,j,INF);
                }
            }
        }
        cout<<g.Maxflow(0,2*m+1)<<endl;
    }
    return 0;
}