题意：给你一张图，有k个人和k个房子，每个房子只能住一个人，每个人到某一房子的花费为曼哈顿距离，问你让k个人怎么走，使他们都住房子且花费最小。

思路：我们把所有人和超级源点相连，流量为1花费为0，所有房子和超级汇点相连，流量为1花费为0，然后把所有人和所有房子加边，流量为1，花费为曼哈顿距离，这样这道题目就变成了求超级源点到超级汇点的MCMF。

代码：

#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include<cstring>
#include<string>
#include<cmath>
#include<cstdlib>
#include<algorithm>
#define ll long long
const int maxn = 10000+5;
const int maxm = 100000+5;
const int MOD = 1e7;
const int INF = 1 << 25;
using namespace std;
struct Edge{int to,next,cap,flow,cost;
}edge[maxm];
struct node{int x,y;
}house[maxn],man[maxn];
int head[maxn],tot;
int pre[maxn],dis[maxn];
bool vis[maxn];
int N,M;
void init(){N = maxn;tot = 0;memset(head,-1,sizeof(head));
}
void addEdge(int u,int v,int cap,int cost){edge[tot].to = v;edge[tot].cap = cap;    //容量edge[tot].flow = 0;edge[tot].cost = cost;edge[tot].next = head[u];head[u] = tot++;edge[tot].to = u;edge[tot].cap = 0;edge[tot].flow = 0;edge[tot].cost = -cost;edge[tot].next = head[v];head[v] = tot++;
}
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);}}}}return pre[t] != -1;
}int MCMF(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 mp[maxn][maxn];
int main(){int n,m;while(scanf("%d%d",&n,&m) && n+m){init();int mcnt = 0,hcnt = 0;for(int i = 1;i <= n;i++){scanf("%s",mp[i] + 1);for(int j = 1;j <= m;j++){if(mp[i][j] == 'm'){man[mcnt].x = i;man[mcnt++].y = j;}else if(mp[i][j] == 'H'){house[hcnt].x = i;house[hcnt++].y = j;}}}//建图for(int i = 1;i <= hcnt;i++){   //和超级源点连addEdge(0,i,1,0);}for(int i = hcnt + 1;i <= 2*hcnt;i++){  //和超级汇点连addEdge(i,2*hcnt + 1,1,0);}for(int i = 0;i < mcnt;i++){for(int j = 0;j < mcnt;j++){int pay = abs(house[i].x - man[j].x) + abs(house[i].y - man[j].y);addEdge(i + 1,j + mcnt + 1,1,pay);}}int cost = 0;MCMF(0,2*hcnt + 1,cost);printf("%d\n",cost);}return 0;
}