Going Home—-最小費用流

題目：http://poj.org/problem?id=2195

原始碼：

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