POJ 1149 PIGS

网络最大流

#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;


const int maxn=2000+10;
const int INF=0x7FFFFFFF;

struct Edge
{
    int from,to,cap,flow;
};
vector<Edge>edges;
vector<int>G[maxn];
bool vis[maxn];
int d[maxn];
int cur[maxn];
int numc[maxn];
int numr[maxn];
int K[maxn][105];
int n,m,s,t;
int N,M,A,LS;

//求出层次网络
bool BFS()
{
    memset(vis,0,sizeof(vis));
    queue<int>Q;
    Q.push(s);
    d[s]=0;
    vis[s]=1;
    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];
}


//加边
void AddEdge(int from,int to,int cap)
{
    Edge r;
    r.from=from;
    r.to=to;
    r.cap=cap;
    r.flow=0;
    edges.push_back(r);
    Edge d;
    d.from=to;
    d.to=from;
    d.cap=0;
    d.flow=0;
    edges.push_back(d);
    m=edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
}

//每个阶段来一次DFS增广
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;
}

//多个阶段，多次建立层次网络。
int Maxflow(int ss,int tt)
{
    int flow=0;
    while(BFS())
    {
        memset(cur,0,sizeof(cur));
        flow+=DFS(ss,INF);
    }
    return flow;
}

int main()
{
    int i,j;
    while(~scanf("%d%d",&M,&N))
    {
        memset(K,0,sizeof(K));
        edges.clear();
        for(int i=0; i<maxn; i++) G[i].clear();
        for(i=1; i<=M; i++) scanf("%d",&numc[i]);
        s=1,t=2+N;
        for(i=2; i<=N+1; i++)
        {
            scanf("%d",&A);
            for(j=1; j<=A; j++)
            {
                scanf("%d",&LS);
                K[LS][0]++;
                K[LS][K[LS][0]]=i;
            }
            scanf("%d",&numr[i]);
        }
        for(i=2; i<=N+1; i++) AddEdge(i,t,numr[i]);
        for(i=1; i<=M; i++)
        {
            for(j=1; j<=K[i][0]; j++)
            {
                if(j==1) AddEdge(1,K[i][j],numc[i]);
                else AddEdge(K[i][j-1],K[i][j],INF);
            }
        }
        printf("%d
",Maxflow(s,t));
    }
    return 0;
}