poj 2195 Going Home

/*
做网络流的题建图真的是太重要了！
本题是将人所在的位置和房子所在的位置建立边的联系，其中man到house这一条边的流量为 1， 费用为两者的距离
而方向边的流量为 0， 费用为正向边的相反数（也就是沿着反向边进行增广时，费用要减少，更改先前错误的选择）
最后增加一个源点和一个汇点完毕（源点映射到man， house映射到汇点， 费用为0， 流量为1）
　　　　


*/
#include<iostream>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<queue>
#define Max 0x3f3f3f3f
#define N 205
using namespace std;

class node
{
public:
int x, y;
};

node xyM
;
node xyH
;
int cost

, cap

;
int cntM, cntH;
int pre[N*2], dist[N*2], vis[N*2], n, m;

void addE(int i, int j, int ct, int cp)
{
cost[i][j]=ct;
cap[i][j]=cp;
cost[j][i]=-ct;
//cap[j][i]=0;
}

int s, t, minCost;

void buildMap()
{
int i, j;
memset(cap, 0, sizeof(cap));
s=0; t=cntM+cntH+1;
for(i=0; i<cntM; ++i)
addE(0, i+1, 0, 1);
for(i=0; i<cntH; ++i)
addE(cntM+i+1, t, 0, 1);
for(i=0; i<cntM; ++i)
for(j=0; j<cntH; ++j)
addE(i+1, cntM+j+1, abs(xyM[i].x-xyH[j].x)+abs(xyM[i].y-xyH[j].y), 1);
}

queue<int>q;

int spfa()
{
int u, v;
memset(dist, 0x3f, sizeof(dist));
dist[0]=0;
q.push(0);
vis[0]=1;
while(!q.empty())
{
u=q.front();
q.pop();
vis[u]=0;
for(v=0; v<=t; ++v)
if(cap[u][v]>0 && dist[v]>dist[u]+cost[u][v])
{
dist[v]=dist[u]+cost[u][v];
pre[v]=u;
if(!vis[v])
{
vis[v]=1;
q.push(v);
}
}
}
if(dist[t]==Max)
return 0;
return 1;
}

void updateEdge()
{
int u, minFlow=Max;
for(u=t; u!=s; u=pre[u])//通过最短路径寻找这条路径上的最小流量
if(cap[pre[u]][u]<minFlow)
minFlow=cap[pre[u]][u];
for(u=t; u!=s; u=pre[u])
{
cap[pre[u]][u]-=minFlow;
cap[u][pre[u]]+=minFlow;
minCost+=cost[pre[u]][u];
}
}

int main()
{
int i, j;
char c;
while(scanf("%d%d", &n, &m) && (n||m))
{
cntM=cntH=0;
minCost=0;
for(i=1; i<=n; ++i)
{
getchar();
for(j=1; j<=m; ++j)
{
scanf("%c", &c);
if(c=='m')
{
xyM[cntM].x=i;
xyM[cntM++].y=j;
}
else if(c=='H')
{
xyH[cntH].x=i;
xyH[cntH++].y=j;
}
}
}
buildMap();
while(spfa())
updateEdge();
printf("%d\n", minCost);
}
return 0;
}

#include<iostream>
#include<queue>
#include<cstring>
#include<cstdio>
#include<algorithm>
#define INF 0x3f3f3f3f
#define N 1000005
using namespace std;

int cntH, cntM;

struct node{
int x, y;
};

struct EDGE{
int u, v, cap, cost, nt;
};
EDGE edge
;

queue<int>q;
node man[105], house[105];
int first[205];
int dist[205];
int pre[205], flow[205], vis[205];
int cnt, t;
int minCost;
int n, m;

void addEdge(int u, int v, int cap, int cost){
edge[cnt].u=u;
edge[cnt].v=v;
edge[cnt].cap=cap;
edge[cnt].nt=first[u];
edge[cnt].cost=cost;
first[u]=cnt++;

edge[cnt].u=v;
edge[cnt].v=u;
edge[cnt].cap=0;
edge[cnt].nt=first[v];
edge[cnt].cost=-cost;
first[v]=cnt++;
}

void buildMap(){
memset(first, -1, sizeof(first));
t=cntH+cntM+1;
for(int i=1; i<=cntM; ++i)
for(int j=1; j<=cntH; ++j)
addEdge(i, cntM+j, 1, abs(man[i].x-house[j].x) + abs(man[i].y-house[j].y));
for(int i=1; i<=cntM; ++i)
addEdge(0, i, 1, 0);
for(int i=1; i<=cntH; ++i)
addEdge(cntM+i, t, 1, 0);
}

bool MCMF(){
memset(dist, 0x3f, sizeof(dist));
memset(vis, 0, sizeof(vis));
q.push(0);
flow[0]=INF;
dist[0]=0;
vis[0]=1;
while(!q.empty()){
int u=q.front(); q.pop();
vis[u]=0;
for(int e=first[u]; ~e; e=edge[e].nt){
int v=edge[e].v, cap=edge[e].cap, cost=edge[e].cost;
if(cap>0 && dist[v]>dist[u]+cost){
dist[v]=dist[u]+cost;
flow[v]=min(flow[u], cap);
pre[v]=e;
if(!vis[v]){
vis[v]=1;
q.push(v);
}
}
}
}
if(dist[t]==INF) return false;
minCost+=dist[t];
int x=t;
while(x!=0){
edge[pre[x]].cap-=flow[t];
edge[pre[x]^1].cap+=flow[t];
x=edge[pre[x]].u;
}
return true;
}

int main(){
while(scanf("%d%d", &n, &m) && (n||m)){
cnt=cntH=cntM=0;
for(int i=1; i<=n; ++i){
getchar();
for(int j=1; j<=m; ++j){
char ch;
scanf("%c", &ch);
if(ch=='m'){
man[++cntM].x=i;
man[cntM].y=j;
}
else if(ch=='H'){
house[++cntH].x=i;
house[cntH].y=j;
}
}
}
buildMap();
minCost=0;
while(MCMF());
printf("%d\n", minCost);
}
return 0;
}