poj3422Kaka's Matrix Travels

http://poj.org/problem?id=3422

最小费用最大流 求的时候把边加为负的 输出的时候再负回来 就变成求的最大费用了

拆点 一个点拆为 i i' i->i'连两条边 一条cap为0 cost为给出的值 另一条cap为INF cost为0 ，i'到右和下分别设置一条边cap为INF cost为0 设置超级源点到1节点 cap为K cost为0

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<stdlib.h>
#include<queue>
#define INF 0xfffffff
#define MN 50500
#define MM 100100
using namespace std;
struct node
{
    int u,v,cost,cap,next;
}edge[MM];
int head[MN],t,vis[MN],dist[MN],pp[MN];
void init()
{
    t  =0;
    memset(head,-1,sizeof(head));
}
void add(int u,int v,int c,int p)
{
    edge[t].u = u;
    edge[t].v = v;
    edge[t].cap = c;
    edge[t].cost = p;
    edge[t].next = head[u];
    head[u] = t++;
    edge[t].u = v;
    edge[t].v = u;
    edge[t].cap = 0;
    edge[t].cost = -p;
    edge[t].next = head[v];
    head[v] = t++;
}
int spfa(int s,int en,int n)
{
    int u,v,i;
    memset(vis,0,sizeof(vis));
    memset(pp,-1,sizeof(pp));
    for(i = 0 ; i <= n ; i++)
    dist[i] =INF;
    queue<int>q;
    dist[s] = 0;
    vis[s] = 1;
    q.push(s);
    while(!q.empty())
    {
        u = q.front();
        q.pop();
        vis[u] = 0;
        //cout<<u<<endl;
        for(i = head[u] ; i != -1 ; i = edge[i].next)
        {
            v = edge[i].v;
            if(edge[i].cap&&dist[v]>dist[u]+edge[i].cost)
            {
                dist[v]  = dist[u]+edge[i].cost;
                pp[v] = i;
                if(!vis[v])
                {
                    vis[v] = 1;
                    q.push(v);
                }
            }
        }
    }
    //cout<<dist[en]<<endl;
    if(dist[en]==INF)
    return 0;
    return 1;
}
int mcmf(int s,int en,int n)
{
    int i,mc=0,minf;
    while(spfa(s,en,n))
    {
        minf = INF+1;
        for(i = pp[en] ; i!= -1 ; i = pp[edge[i].u])
        {
            if(minf>edge[i].cap)
            minf = edge[i].cap;
        }
        for(i = pp[en] ; i != -1; i = pp[edge[i].u])
        {
            edge[i].cap -= minf;
            edge[i^1].cap+=minf;
        }
        //cout<<minf<<" "<<dist[en]<<endl;
        mc+=minf*dist[en];
    }
    return mc;
}
int main()
{
    int i,j,k,n,m,a;
    while(cin>>n>>k)
    {
        init();
        int s = 0,en = 2*n*n+1;
        add(s,1,k,0);
        add(2*n*n,en,k,0);
        for(i = 1; i <= n ; i++)
            for(j = 1; j <= n ; j++)
            {
                cin>>a;
                add((i-1)*n+j,(i-1)*n+j+n*n,1,-a);
                add((i-1)*n+j,(i-1)*n+j+n*n,INF,0);
                if(i<n)
                add((i-1)*n+j+n*n,i*n+j,INF,0);
                if(j<n)
                add((i-1)*n+j+n*n,(i-1)*n+j+1,INF,0);
            }
        cout<<-mcmf(s,en,en)<<endl;
    }
    return 0;
}