1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143
|
#include<iostream> #include<cstdio> #include<cstring> #include<queue> using namespace std; const int MAX_POINT=40023; const int MAX_EDGE=400024; const int MAX_POS=206; const int inf=0x3f3f3f3f;
const int dx[]={-2,-2,-1,-1,1,1,2,2}; const int dy[]={-1,1,-2,2,-2,2,-1,1}; bool forbidden[MAX_POS][MAX_POS]; struct E { int to; int cap; int Next=-1; }edge[MAX_EDGE]; int head[MAX_POINT],tot; int s,t; int depth[MAX_POINT]; int n,m; void init(); inline void add_edge(int,int,int); inline int ID(int,int); bool bfs(); int dfs(int,int); int Dinic(); int main() { int i,j,k; cin>>n>>m; int sum=n*n-m; init(); for(i=1;i<=m;i++) { int x,y; scanf("%d%d",&x,&y); forbidden[x][y]=1; } for(i=1;i<=n;i++) { for(j=1;j<=n;j++) { if(forbidden[i][j]) continue; if((i+j)&1) add_edge(ID(i,j),t,1); else { add_edge(s,ID(i,j),1); for(k=0;k<8;k++) { int x=i+dx[k]; int y=j+dy[k]; if(x<1||x>n||y<1||y>n) continue; if(forbidden[x][y]) continue; add_edge(ID(i,j),ID(x,y),inf); } } } } cout<<sum-Dinic()<<endl; return 0; } void init() { tot=1; memset(head,-1,sizeof(head)); s=0; t=n*n+1; } inline int ID(int x,int y) {return (x-1)*n+y;} inline void add_edge(int u,int v,int cap) { tot++; edge[tot].to=v; edge[tot].cap=cap; edge[tot].Next=head[u]; head[u]=tot; tot++; edge[tot].to=u; edge[tot].cap=0; edge[tot].Next=head[v]; head[v]=tot; } bool bfs() { memset(depth,0,sizeof(depth)); queue<int>q; q.push(s); depth[s]=1; while(!q.empty()) { int x=q.front(); q.pop(); for(register int i=head[x];~i;i=edge[i].Next) { int y=edge[i].to; if(edge[i].cap&&!depth[y]) { q.push(y); depth[y]=depth[x]+1; if(y==t) return 1; } } } return 0; } int dfs(int x,int flow) { if(x==t) return flow; int rest=flow; int temp; for(register int i=head[x];~i&&rest;i=edge[i].Next) { int y=edge[i].to; if(edge[i].cap&&depth[y]==depth[x]+1) { temp=dfs(y,min(rest,edge[i].cap)); if(!temp) depth[y]=0; edge[i].cap-=temp; edge[i^1].cap+=temp; rest-=temp; } } return flow-rest; } int Dinic() { int maxflow=0; while(bfs()) maxflow+=dfs(s,inf); return maxflow; }
|