bzoj 3171 [Tjoi2013]循环格（MCMF）

  1 #include<set>
  2 #include<cmath>
  3 #include<queue>
  4 #include<vector>
  5 #include<cstdio>
  6 #include<cstring>
  7 #include<iostream>
  8 #include<algorithm>
  9 #define trav(u,i) for(int i=front[u];i;i=e[i].nxt)
 10 #define FOR(a,b,c) for(int a=(b);a<=(c);a++)
 11 using namespace std;
 12 
 13 typedef long long ll;
 14 const int N = 1e3+10;
 15 const int inf = 1e9;
 16 
 17 ll read() {
 18     char c=getchar();
 19     ll f=1,x=0;
 20     while(!isdigit(c)) {
 21         if(c==‘-‘) f=-1; c=getchar();
 22     }
 23     while(isdigit(c))
 24         x=x*10+c-‘0‘,c=getchar();
 25     return x*f;
 26 }
 27 
 28 struct Edge {
 29     int u,v,cap,flow,cost;
 30 };
 31 struct MCMF {
 32     int n,m,s,t;
 33     int a[N],p[N],inq[N],d[N];
 34     vector<Edge> es;
 35     vector<int> g[N];
 36     queue<int> q;
 37     void init(int n) {
 38         this->n=n;
 39         es.clear();
 40         FOR(i,0,n) g[i].clear();
 41     }
 42     void AddEdge(int u,int v,int w,int c) {
 43         es.push_back((Edge){u,v,w,0,c});
 44         es.push_back((Edge){v,u,0,0,-c});
 45         int m=es.size();
 46         g[u].push_back(m-2);
 47         g[v].push_back(m-1);
 48     }
 49     int spfa(int s,int t,int& flow,int& cost) {
 50         memset(inq,0,sizeof(inq));
 51         FOR(i,0,n) d[i]=inf;
 52         inq[s]=1; d[s]=0; a[s]=inf; p[s]=0; 
 53         q.push(s);
 54         while(!q.empty()) {
 55             int u=q.front(); q.pop(); inq[u]=0;
 56             FOR(i,0,(int)g[u].size()-1) {
 57                 Edge& e=es[g[u][i]];
 58                 int v=e.v;
 59                 if(d[v]>d[u]+e.cost && e.cap>e.flow) {
 60                     d[v]=d[u]+e.cost;
 61                     a[v]=min(a[u],e.cap-e.flow);
 62                     p[v]=g[u][i];
 63                     if(!inq[v])
 64                         inq[v]=1,q.push(v);
 65                 }
 66             }
 67         }
 68         if(d[t]==inf) return 0;
 69         flow+=a[t]; cost+=a[t]*d[t];
 70         for(int x=t;x!=s;x=es[p[x]].u) {
 71             es[p[x]].flow+=a[t];
 72             es[p[x]^1].flow-=a[t];
 73         }
 74         return 1;
 75     }
 76     void mcmf(int s,int t,int&flow,int&cost) {
 77         flow=cost=0;
 78         while(spfa(s,t,flow,cost)) ;
 79     }
 80 } mc;
 81 
 82 const char dir[]={‘L‘,‘R‘,‘U‘,‘D‘};
 83 const int dx[]={0,0,-1,1};
 84 const int dy[]={-1,1,0,0};
 85 int n,m,S,T;
 86 char mp[N][N];
 87 
 88 int id(int x,int y) { return (x-1)*m+y; }
 89 
 90 int main()
 91 {
 92     n=read(),m=read();
 93     FOR(i,1,n) scanf("%s",mp[i]+1);
 94     mc.init(n*m*2+2);
 95     S=0,T=n*m*2+1;
 96     FOR(i,1,n) {
 97         FOR(j,1,m) {
 98             FOR(d,0,3) {
 99                 int x=i+dx[d],y=j+dy[d];
100                 x=(x-1+n)%n+1,y=(y-1+m)%m+1;
101                 if(dir[d]==mp[i][j])
102                     mc.AddEdge(id(i,j),id(x,y)+n*m,1,0);
103                 else mc.AddEdge(id(i,j),id(x,y)+n*m,1,1);
104             }
105             mc.AddEdge(S,id(i,j),1,0);
106             mc.AddEdge(id(i,j)+n*m,T,1,0);
107         }
108     }
109     int cost,flow;
110     mc.mcmf(S,T,flow,cost);
111     printf("%d",cost);
112     return 0;
113 }