poj 1459 Power Network， 最大流，多源多匯

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點擊開啟連結

 多源多匯最大流，虛擬一個源點s‘和一個匯點t‘，原來的源點、匯點向它們連邊。

#include<cstdiO>#include<cstring>#include<iostream>#include<algorithm>#include<queue>#include<vector>using namespace std;const int maxn = 500 + 5;const int INF = 100000000;struct Edge{    int from, to, cap, flow;};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});        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 solver;int main(){    int n, np, nc, m;    char ch;    int x, y, z;    while(~scanf("%d%d%d%d", &n, &np, &nc, &m))    {        int s = 0, t = n+1;        solver.init(t+2);        for(int i=1; i<=m; ++i)        {            cin>>ch>>x>>ch>>y>>ch>>z;            if(x==y) continue;            solver.AddEdge(x+1, y+1, z);        }        for(int i=1; i<=np; ++i)        {            cin>>ch>>x>>ch>>z;            solver.AddEdge(s, x+1, z);        }        for(int i=1; i<=nc; ++i)        {            cin>>ch>>x>>ch>>z;            solver.AddEdge(x+1, t, z);        }        int ans = solver.Maxflow(s,t);        printf("%d\n", ans);    }    return 0;}