uva 11380(最大流+拆点）

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=36707

思路：根据题意拆点建图即可。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<queue>
 using namespace std;
 #define MAXN 2222
 #define inf 1<<30
 
 struct Edge{
     int v,cap,next;
 }edge[MAXN*MAXN];
 
 int n,m,p,NE,NV,vs,vt;
 int head[MAXN];
 
 void Insert(int u,int v,int cap)
 {
     edge[NE].v=v;
     edge[NE].cap=cap;
     edge[NE].next=head[u];
     head[u]=NE++;
 
     edge[NE].v=u;
     edge[NE].cap=;
     edge[NE].next=head[v];
     head[v]=NE++;
 }
 
 int level[MAXN],gap[MAXN];
 void bfs(int vt)
 {
     memset(level,-,sizeof(level));
     memset(gap,,sizeof(gap));
     level[vt]=;
     gap[]++;
     queue<int>que;
     que.push(vt);
     while(!que.empty()){
         int u=que.front();
         que.pop();
         for(int i=head[u];i!=-;i=edge[i].next){
             int v=edge[i].v;
             if(level[v]!=-)continue;
             level[v]=level[u]+;
             gap[level[v]]++;
             que.push(v);
         }
     }
 }
 
 int cur[MAXN],pre[MAXN];
 int SAP(int vs,int vt)
 {
     bfs(vt);
     memset(pre,-,sizeof(pre));
     memcpy(cur,head,sizeof(head));
     int u=pre[vs]=vs,aug=inf,maxflow=;
     gap[]=NV;
     while(level[vs]<NV){
         bool flag=false;
         for(int &i=cur[u];i!=-;i=edge[i].next){
             int v=edge[i].v;
             if(edge[i].cap>&&level[u]==level[v]+){
                 flag=true;
                 aug=min(aug,edge[i].cap);
                 pre[v]=u;
                 u=v;
                 if(v==vt){
                     maxflow+=aug;
                     for(u=pre[u];v!=vs;v=u,u=pre[u]){
                         edge[cur[u]].cap-=aug;
                         edge[cur[u]^].cap+=aug;
                     }
                     aug=inf;
                 }
                 break;
             }
         }
         if(flag)continue;
         int minlevel=NV;
         for(int i=head[u];i!=-;i=edge[i].next){
             int v=edge[i].v;
             if(edge[i].cap>&&level[v]<minlevel){
                 minlevel=level[v];
                 cur[u]=i;
             }
         }
         if(--gap[level[u]]==)break;
         level[u]=minlevel+;
         gap[level[u]]++;
         u=pre[u];
     }
     return maxflow;
 }
 
 char map[][];
 int dir[][]={{-,},{,},{,-},{,}};
 
 int main()
 {
     while(~scanf("%d%d%d",&n,&m,&p)){
         for(int i=;i<n;i++)scanf("%s",map[i]);
         NE=;
         vs=,vt=*n*m+,NV=*n*m+;
         memset(head,-,sizeof(head));
         for(int i=;i<n;i++){
             for(int j=;j<m;j++){
                 if(map[i][j]=='~')continue;
                 for(int k=;k<;k++){
                     int x=i+dir[k][],y=j+dir[k][];
                     if(x<||x>=n||y<||y>=m)continue;
                     Insert(i*m+j++n*m,x*m+y+,inf);
                 }
                 if(map[i][j]=='*'){
                     Insert(vs,i*m+j+,);
                     Insert(i*m+j+,i*m+j++n*m,);
                 }
                 else if(map[i][j]=='.')Insert(i*m+j+,i*m+j++n*m,);
                 else if(map[i][j]=='@')Insert(i*m+j+,i*m+j++n*m,inf);
                 else if(map[i][j]=='#')Insert(i*m+j+,i*m+j++n*m,inf),Insert(i*m+j++n*m,vt,p);
             }
         }
         printf("%d\n",SAP(vs,vt));
     }
     return ;
 }