POJ2195 Going Home[费用流|二分图最大权匹配]

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long ll;
const int N=5005,M=1e6+5,INF=1e9;
int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1; c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘; c=getchar();}
    return x*f;
}
int n,m,s,t,n1,n2;
char ss[105];
struct data{
    int x,y;
}a[N],b[N];
inline int dis(data &a,data &b){return abs(a.x-b.x)+abs(a.y-b.y);}

struct edge{
    int v,ne,c,f,w;
}e[M<<1];
int cnt,h[N];
inline void ins(int u,int v,int c,int w){
    cnt++;
    e[cnt].v=v;e[cnt].c=c;e[cnt].f=0;e[cnt].w=w;
    e[cnt].ne=h[u];h[u]=cnt;
    cnt++;
    e[cnt].v=u;e[cnt].c=0;e[cnt].f=0;e[cnt].w=-w;
    e[cnt].ne=h[v];h[v]=cnt;
}
void build(){
    cnt=0;
    memset(h,0,sizeof(h));
    s=0;t=n1+n2+1;
    for(int i=1;i<=n1;i++)
        for(int j=1;j<=n2;j++) ins(i,n1+j,1,dis(a[i],b[j]));
    for(int i=1;i<=n1;i++) ins(s,i,1,0);
    for(int i=1;i<=n2;i++) ins(n1+i,t,1,0);
}
int d[N],q[N],head,tail,inq[N],pre[N],pos[N];
inline void lop(int &x){if(x==N)x=1;}
bool spfa(){
    memset(d,127,sizeof(d));
    memset(inq,0,sizeof(inq));
    head=tail=1;
    d[s]=0;inq[s]=1;q[tail++]=s;
    pre[t]=-1;
    while(head!=tail){
        int u=q[head++];inq[u]=0;lop(head);
        for(int i=h[u];i;i=e[i].ne){
            int v=e[i].v,w=e[i].w;
            if(d[v]>d[u]+w&&e[i].c>e[i].f){
                d[v]=d[u]+w;
                pre[v]=u;pos[v]=i;
                if(!inq[v])q[tail++]=v,inq[v]=1,lop(tail); 
            }
        }
    }
    return pre[t]!=-1;
}
int mcmf(){
    int flow=0,cost=0;
    while(spfa()){
        int f=INF;
        for(int i=t;i!=s;i=pre[i]) f=min(f,e[pos[i]].c-e[pos[i]].f);
        flow+=f;cost+=d[t]*f;
        for(int i=t;i!=s;i=pre[i]){
            e[pos[i]].f+=f;
            e[((pos[i]-1)^1)+1].f-=f;
        }
    }
    return cost;
}
int main(int argc, const char * argv[]){
    while(true){
        n1=n2=0;
        n=read();m=read();
        if(n==0&&m==0) break;
        for(int i=1;i<=n;i++){
            scanf("%s",ss+1);
            for(int j=1;j<=m;j++){
                if(ss[j]==‘H‘) a[++n1]=(data){i,j};
                if(ss[j]==‘m‘) b[++n2]=(data){i,j};
            }
        }
        build();
        printf("%d\n",mcmf());
    }
}