POJ 1459 Power Network

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最大流问题。

题意说电网有三种站点，发电站，中转站，用户站。直接建立超级S 和 T 。

S-> 发电站容量就是发电量。用户-> T 容量就是用电量。

然后求最大流即可。

#include<cstdio>#include<cstring>#include<string>#include<queue>#include<algorithm>#include<map>#include<stack>#include<iostream>#include<list>#include<set>#include<cmath>#define INF 0x7fffffff#define eps 1e-6#define LL long long#define acfun std::ios::sync_with_stdio(false)using namespace std;int n,np,nc,m;struct lx{    int c,f;};lx g[301][301];bool vis[301];int path[301];int flow[301];void EK(int start,int thend){    int maxflow=0;    while(1)    {        for(int i=0;i<n+2;i++)            vis[i]=0,path[i]=-1,flow[i]=0;        queue<int>q;        q.push(start);        vis[start]=1,flow[start]=INF;        while(!q.empty()&&!vis[thend])        {            int u=q.front();q.pop();            for(int j=0;j<n+2;j++)            {                if(vis[j])continue;                if(g[u][j].f<g[u][j].c)                {                    vis[j]=1;                    path[j]=u;                    flow[j]=min(flow[u],g[u][j].c-g[u][j].f);                    q.push(j);                }                else if(g[j][u].f>0)                {                    vis[j]=1;                    path[j]=u;                    flow[j]=min(flow[u],g[j][u].f);                    q.push(j);                }            }        }        if(!vis[thend]||flow[thend]==0)break;        int v=thend,u=path[thend];        int tmp=flow[thend];        maxflow+=tmp;        while(u!=-1)        {            if(g[u][v].f<g[u][v].c)                g[u][v].f+=tmp;            else                g[v][u].f-=tmp;            v=u,u=path[v];        }    }    printf("%d\n",maxflow);}int main(){    while(scanf("%d%d%d%d",&n,&np,&nc,&m)!=EOF)    {        for(int i=0;i<n+2;i++)            for(int j=0;j<n+2;j++)            g[i][j].c=g[i][j].f=0;        int u,v,c;        char str[1001];        while(m--)        {            scanf("%s",str);            sscanf(str,"(%d,%d)%d",&u,&v,&c);            g[u][v].c=c;        }        for(int i=0;i<np;i++)        {            scanf("%s",str);            sscanf(str,"(%d)%d",&v,&c);            g[n][v].c=c;        }        for(int i=0;i<nc;i++)        {            scanf("%s",str);            sscanf(str,"(%d)%d",&u,&c);            g[u][n+1].c=c;        }        EK(n,n+1);    }}

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