GYM 101128 F.Landscaping(网络流)

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<vector>
 5 #include<queue>
 6 using namespace std;
 7 const int delta=50;
 8 const int maxn=2505,inf=1e9+5;
 9 char field[55][55];
10 struct Edge{
11     int from,to,cap,flow;
12     Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f){}
13 };
14 struct EdmodsKarp{
15     int n;
16     vector<Edge> edges;
17     vector<int> G[maxn];
18     int a[maxn];
19     int p[maxn];
20     void init(int n){
21         for(int i=0;i<n;i++)G[i].clear();
22         edges.clear();
23         this->n=n;
24     }
25     void AddEdge(int from,int to,int cap){
26         edges.push_back(Edge(from,to,cap,0));
27         edges.push_back(Edge(to,from,0,0));
28         G[from].push_back(edges.size()-2);
29         G[to].push_back(edges.size()-1);
30     }
31     int Maxflow(int s,int t){
32         int flow=0;
33         while(1){
34             memset(a,0,sizeof(a));
35             queue<int> Q;
36             Q.push(s);
37             a[s]=inf;
38             while(!Q.empty()){
39                 int x=Q.front();Q.pop();
40                 for(int i=0;i<G[x].size();i++){
41                     Edge &e=edges[G[x][i]];
42                     if(!a[e.to]&&e.cap>e.flow){
43                         p[e.to]=G[x][i];
44                         a[e.to]=min(a[x],e.cap-e.flow);
45                         Q.push(e.to);
46                     }
47                 }
48                 if(a[t])break;
49             }
50             if(!a[t])break;
51             for(int u=t;u!=s;u=edges[p[u]].from){
52                 edges[p[u]].flow+=a[t];
53                 edges[p[u]^1].flow-=a[t];
54             }
55             flow+=a[t];
56         }
57         return flow;
58     }
59 }ek;
60 void add(int s,int t,int cap){
61     ek.AddEdge(s,t,cap);
62     ek.AddEdge(t,s,cap);
63 }
64 int main(){
65 //    freopen("e:\\in.txt","r",stdin);
66     int n,m,a,b;
67     scanf("%d%d%d%d",&n,&m,&a,&b);
68     ek.init(m*n+2);
69     for(int i=0;i<n;i++){
70         for(int j=0;j<m;j++){
71             cin>>field[i][j];
72         }
73     }
74     for(int i=0;i<n;i++){
75         for(int j=0;j<m;j++){
76             if(i<n-1){
77                 add(i*delta+j,(i+1)*delta+j,a);
78             }
79             if(j<m-1){
80                 add(i*delta+j,i*delta+j+1,a);
81             }
82             if(field[i][j]==‘#‘)
83                 ek.AddEdge(i*delta+j,delta*delta+1,b);
84             else
85                 ek.AddEdge(delta*delta,i*delta+j,b);
86         }
87     }
88     printf("%d\n",ek.Maxflow(delta*delta,delta*delta+1));
89     return 0;
90 }