Going Home----最小費用流

題目：http://poj.org/problem?id=2195

源代碼：

#include <stdio.h>
#define INF 1e9
#define MAXN 150
#define N 300
#define M  30000

int n,m;

int numH,numM,num,ans;

char str[MAXN][MAXN];

int Hx[MAXN],Hy[MAXN],Mx[MAXN],My[MAXN];

int min(int a,int b)
{
  return a>b?b:a;
}

struct MinCostMaxFlow {
    int e, ev[M], nxt[M], head[N];
    int  cost[M], dist[N];
    int cap[M];
    int pnt[N], road[N], q[N], bg, ed;
    bool vis[N];

 void init(int n) {
   e = 0;
   for(int i=0;i<=n;i++)
    head[i]=-1;
  }

 void addedge(int u, int v, int f, int  c) { //u->v flow=f, cost=c
   ev[e]=v; cap[e]=f; cost[e]=c; nxt[e]=head[u]; head[u]=e++;
   ev[e]=u; cap[e]=0; cost[e]=-c; nxt[e]=head[v]; head[v]=e++;
   }

 bool spfa(int s, int t, int n) {
     for(int i=0;i<=n;i++)  {  dist[i]=INF;  vis[i]=0; }
     bg = ed = dist[s] = 0;
     pnt[s] = s; q[ed++] = s;
     while (bg != ed) {
         int u = q[bg++]; vis[u] = 0;
         if (bg == N) bg = 0;
         for (int i = head[u]; ~i; i = nxt[i]) {
            if (cap[i] <= 0)  continue;
            int v = ev[i];
            if (dist[v] > dist[u] + cost[i]) {
                dist[v] = dist[u] + cost[i];
                pnt[v] = u; road[v] = i;
            if (!vis[v]) {
                q[ed++] = v; vis[v] = 1;
                if(ed == N)ed = 0;
                }
            }
        }
    }
    return dist[t] != INF;
}

 void mincost(int s, int t, int n, int &f, int  &c) {
        c = f = 0;
        while(spfa(s, t, n)){
            int minf = INF;
            for(int u = t; u != s; u = pnt[u])
                minf = min(minf, cap[road[u]]);
                for(int u = t; u != s; u = pnt[u]){
                    cap[road[u]] -= minf;
                    cap[road[u] ^ 1] += minf;
                    }
                f += minf;
                c += minf * dist[t];
            }
    }
};

int abs(int a)
{
    if(a<0)  return -a;
    return a;
}

int solve()
{
    MinCostMaxFlow tmp;
    int ans,ans1,d;
    tmp.init(2*num+2);
    for(int i=0;i<num;i++)
    tmp.addedge(0,i+1,1,0);
    for(int i=0;i<num;i++)
    tmp.addedge(i+1+num,2*num+1,1,0);
    for(int i=0;i<num;i++)
      for(int j=0;j<num;j++)
      {
          d=abs(Hx[i]-Mx[j])+abs(Hy[i]-My[j]);
          tmp.addedge(i+1,j+1+num,INF,d);
      }
    tmp.mincost(0,2*num+1,2*num+2,ans1,ans);
    return ans;
}


int main()
{
    freopen("D:\\a.txt","r",stdin);
    while(true)
    {
        scanf("%d %d",&n,&m);
        if(!m&&!n)  break;
        for(int i=0;i<n;i++)
        scanf("%s",str[i]);
        numH=0;  numM=0;
        for(int i=0;i<n;i++)
          for(int j=0;j<m;j++)
          {
              if(str[i][j]=='H')
               {
                   Hx[numH]=i;  Hy[numH]=j;
                   numH++;
               }
              if(str[i][j]=='m')
               {
                   Mx[numM]=i;  My[numM]=j;
                   numM++;
               }
          }
       if(numH==numM)  num=numH;
       ans=solve();
       printf("%d\n",ans);
    }
}