hdu 1533 Going Home

This is my first min_cost network max_flow problems;

From start_point to every 'm' point ,capacity is 1,cost is 0;

From 'H' point to end_point .capacity is 1,cost is 0;

From 'm' point to every 'H' point.capacity is 1,cost is manhattan distance of 'm' point and 'H' point;

The portal:http://acm.hdu.edu.cn/showproblem.php?pid=1533  

#include <cstdio>
#include <cstdlib>
#include <queue>
#include <cmath>
#include <cstring>

using namespace std;

const int MAXN = 10000;
const int MAXM = 100000;
const int INF = 0x3f3f3f3f;

struct Edge{
    int to,next,cap,flow,cost;
}edge[MAXM];

int head[MAXN],tol;
int pre[MAXN],dis[MAXN];
bool vis[MAXN];
int N;
//N means the number of nodes.from 0 to n-1

void init(int n){
    N = n;
    tol = 0;
    memset(head,-1,sizeof(head));
}

void addedge(int u,int v,int cap,int cost){
    edge[tol].to = v; edge[tol].cap = cap; edge[tol].cost = cost;
    edge[tol].flow = 0; edge[tol].next = head[u]; head[u] = tol ++;
    edge[tol].to = u; edge[tol].cap = 0; edge[tol].cost = -cost;
    edge[tol].flow = 0; edge[tol].next = head[v]; head[v] = tol ++;
}

bool spfa(int s,int t){
    queue<int>q;
    for(int i = 0;i < N;i++){
        dis[i] = INF;
        vis[i] = false;
        pre[i] = -1;
    }
    dis[s] = 0;
    vis[s] = true;
    q.push(s);
    while(!q.empty()){
        int u = q.front();
        q.pop();
        vis[u] = false;
        for(int i=head[u];i != -1;i=edge[i].next){
            int v = edge[i].to;
            if(edge[i].cap > edge[i].flow && dis[v] > dis[u] + edge[i].cost){
                dis[v] = dis[u] + edge[i].cost;
                pre[v] = i;
                if(!vis[v]){
                    vis[v] = true;
                    q.push(v);
                }
            }
        }
    }
    if(pre[t] == -1) return false;
    else return true;
}

//ruturn maxflow ,cost is the mincost;
int mincost_maxflow(int s,int t,int &cost){
    int flow = 0;
    cost = 0;
    while(spfa(s,t)){
        int Min = INF;
        for(int i = pre[t];i != -1;i = pre[edge[i^1].to]){
            if(Min > edge[i].cap - edge[i].flow)
                Min = edge[i].cap - edge[i].flow;
        }
        for(int i = pre[t];i != -1;i = pre[edge[i^1].to]){
            edge[i].flow += Min;
            edge[i^1].flow -= Min;
            cost += edge[i].cost * Min;
        }
        flow += Min;
    }
    return flow;
}

char Map[105][105];
int mat[105][105];

void Deal_with(void){
    int n,m;
    while(scanf("%d %d",&n,&m),n+m){
        //init();
        int start_point = 0;
        int total = 0;
        memset(Map,0,sizeof(Map));
        memset(mat,0,sizeof(mat));
        for(int i=0;i<n;i++){
            scanf("%s",Map[i]);
            for(int j=0;j<m;j++){
                if(Map[i][j] == 'm' || Map[i][j] == 'H'){
                    mat[i][j] = ++ total;
                }
            }
        }
        int end_point = ++ total;
        init(total+1);
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(Map[i][j] == 'H'){
                    addedge(mat[i][j],end_point,1,0);
                }
                if(Map[i][j] == 'm'){
                    addedge(start_point,mat[i][j],1,0);
                    for(int ii=0;ii<n;ii++){
                        for(int jj=0;jj<m;jj++){
                            if(Map[ii][jj] == 'H'){
                                int t_cost = abs(i-ii) + abs(j-jj);
                                addedge(mat[i][j],mat[ii][jj],1,t_cost);
                            }
                        }
                    }
                }
            }
        }
        int min_cost;
        mincost_maxflow(start_point,end_point,min_cost);
        printf("%d\n",min_cost);
    }
}

int main(void){
    //freopen("a.in","r",stdin);
    Deal_with();
    return 0;
}