POJ1459(最大流Isap)

题意:有一个电力网络,有发电厂,有用户,图提供的信息有发电厂和用户的容量,还有边,以及边的容量和流量,求解用户的最大使用量.

先输入四个数 n np nc m,n表示的是总共的顶点数目,np表示发电厂的数目,nc表示用户的数目,m表示边数.

再输入m条边的信息,再输入np个发电厂的信息,再输入nc个用户的信息

(1)对输入的m条边建边

(2)对源点到每个发电站建边

(3)对每个用户到汇点建边

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
using namespace std;
#define inf 0x7fffffff
#define N 300
#define M 30000
int cur[N],pre[N],gap[N],dis[N];
int size,head[N];
struct Edge
{
    int v,w,next;
    Edge(){}
    Edge(int V,int W,int NEXT):v(V),w(W),next(NEXT){}
}edge[M];
void Init()
{
    size = 0;
    memset(head,-1,sizeof(head));
}
void InsertEdge(int u,int v,int w)
{
    edge[size] = Edge(v,w,head[u]);
    head[u] = size++;
    edge[size] = Edge(u,0,head[v]);
    head[v] = size++;
}
int Isap(int st,int ed,int n)
{
    for(int i=0; i<=n; i++)
    {
        cur[i] = head[i];
        gap[i] = dis[i] = 0;
    }
    int u = pre[st] = st;
    int aug = inf ,maxflow = 0;
    while(dis[st] < n)
    {
        loop:
        for(int &i=cur[u]; i!=-1; i=edge[i].next)
        {
            int v = edge[i].v;
            if(edge[i].w && dis[u]==dis[v]+1)
            {
                aug = min(aug,edge[i].w);
                pre[v] = u;
                u = v;
                if(v==ed)
                {
                    maxflow += aug;
                    for(u=pre[u]; v!=st; v=u,u=pre[u])
                    {
                        edge[cur[u]].w -= aug;
                        edge[cur[u]^1].w += aug;
                    }
                    aug = inf;
                }
                goto loop;
            }
        }
        int mindis = n;
        for(int i=head[u]; i!=-1; i=edge[i].next)
        {
            int v = edge[i].v;
            if(edge[i].w && dis[v] < mindis)
            {
                cur[u] = i;
                mindis = dis[v];
            }
        }
        if(--gap[dis[u]]==0) break;
        gap[dis[u]=mindis+1]++;
        u = pre[u];
    }
    return maxflow;
}
int main()
{
    int n,np,nc,m,st,ed,nv,u,v,w;
    char s[15];
    while(scanf("%d%d%d%d",&n,&np,&nc,&m)!=EOF)
    {
        Init(); nv = n+2; st = n ; ed = n+1;
        for(int i=1; i<=m; i++)
        {
            scanf("%s",s);
            sscanf(s,"(%d,%d)%d",&u,&v,&w); //学到了,sscanf分离字符串中的数字 
            InsertEdge(u,v,w);
        }
        for(int i=1; i<=np; i++)
        {
            scanf("%s",s);
            sscanf(s,"(%d)%d",&v,&w);
            InsertEdge(st,v,w);
        }
        
        for(int i=1; i<=nc; i++)
        {
            scanf("%s",s);
            sscanf(s,"(%d)%d",&u,&w);
            InsertEdge(u,ed,w);
        }
        printf("%d
",Isap(st,ed,nv));
    }
    return 0;
}