POJ 2749
二分+2SAT的题
写错了HIGH和LOW与MID的变换，TLE了好几次。。
按HATE和LIKE关系先加边，再用距离的限制加边。
dist(i,S1)+dist(S1,j)>limit Xi->~Xj Xj->Xi
dist(i,S2)+dist(S2,j)>limit ~Xi->Xj ~Xj->Xi
dist(i,S1)+dist(S1,S2)+dist(S2,j)>limit Xi->Xj ~Xj->~Xi
dist(i,S2)+dist(S2,S1)+dist(S1,j)>limit ~Xi->~Xj Xj->Xi
用离散数学的知识就能推出来，以上借别人的一用。
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <algorithm> 5 #include <cmath> 6 7 using namespace std; 8 9 const int inf=8500000; 10 const int MAXN=1050; 11 const int MAXM=20000000; 12 int s1_s2,dis1[MAXN],dis2[MAXN],head[MAXN],dfn[MAXN],low[MAXN],belong[MAXN]; 13 int st[MAXN],stop,indx,tot,pat; 14 bool stack[MAXN]; int leng; 15 int n,hn,ln; 16 struct d{ 17 int x,y; 18 }point[MAXN],s1,s2; 19 struct h{ 20 int u,v; 21 }hate[MAXN*2]; 22 struct l{ 23 int u,v; 24 }like[MAXN*2]; 25 26 struct ei{ 27 int u,v; 28 int next; 29 }edge[MAXM]; 30 31 void addedge(int u,int v){ 32 edge[tot].u=u; 33 edge[tot].v=v; 34 edge[tot].next=head[u]; 35 head[u]=tot++; 36 } 37 38 void tarjan(int u){ 39 int v; 40 dfn[u]=low[u]=++indx; 41 st[stop++]=u; 42 stack[u]=true; 43 for(int e=head[u];e!=-1;e=edge[e].next){ 44 v=edge[e].v; 45 if(dfn[v]==0){ 46 tarjan(v); 47 low[u]=min(low[u],low[v]); 48 } 49 else if(stack[v]){ 50 low[u]=min(low[u],dfn[v]); 51 } 52 } 53 if(dfn[u]==low[u]){ 54 pat++; 55 do{ 56 v=st[--stop]; 57 stack[v]=false; 58 belong[v]=pat; 59 }while(u!=v); 60 } 61 } 62 63 bool slove(){ 64 int u,v; 65 66 memset(head,-1,sizeof(head)); 67 memset(dfn,0,sizeof(dfn)); 68 memset(low,0,sizeof(low)); 69 memset(belong,0,sizeof(belong)); 70 stop=0; indx=0; tot=0; pat=0; 71 memset(stack,false,sizeof(stack)); 72 73 74 for(int i=0;i<hn;i++){ 75 u=hate[i].u; 76 v=hate[i].v; 77 addedge(u*2,v*2+1); 78 addedge(v*2,u*2+1); 79 addedge(2*u+1,2*v); 80 addedge(2*v+1,2*u); 81 } 82 for(int i=0;i<ln;i++){ 83 u=like[i].u; 84 v=like[i].v; 85 addedge(u*2,v*2); 86 addedge(v*2,u*2); 87 addedge(2*u+1,2*v+1); 88 addedge(2*v+1,2*u+1); 89 } 90 for(int i=0;i<n;i++){ 91 for(int j=i+1;j<n;j++){ 92 if(dis1[i]+dis1[j]>leng){ 93 addedge(i*2,j*2+1); 94 addedge(j*2,i*2+1); 95 } 96 if(dis2[i]+dis2[j]>leng){ 97 addedge(i*2+1,j*2); 98 addedge(j*2+1,i*2); 99 } 100 if(dis1[i]+s1_s2+dis2[j]>leng){ 101 addedge(i*2,j*2); 102 addedge(j*2+1,i*2+1); 103 } 104 if(dis2[i]+s1_s2+dis1[j]>leng){ 105 addedge(j*2,i*2); 106 addedge(i*2+1,j*2+1); 107 } 108 } 109 } 110 for(int i=0;i<2*n;i++){ 111 if(dfn[i]==0) 112 tarjan(i); 113 } 114 bool flag=true; 115 for(int i=0;i<n;i++){ 116 if(belong[2*i]==belong[2*i+1]){ 117 flag=false; 118 break; 119 } 120 } 121 return flag; 122 } 123 124 int main(){ 125 int u,v; int tmp; 126 while(scanf("%d%d%d",&n,&hn,&ln)!=EOF){ 127 scanf("%d%d%d%d",&s1.x,&s1.y,&s2.x,&s2.y); 128 for(int i=0;i<n;i++){ 129 scanf("%d%d",&point[i].x,&point[i].y); 130 } 131 for(int i=0;i<hn;i++){ 132 scanf("%d%d",&u,&v); 133 u--; v--; 134 hate[i].u=u; hate[i].v=v; 135 } 136 for(int i=0;i<ln;i++){ 137 scanf("%d%d",&u,&v); 138 u--; v--; 139 like[i].u=u; like[i].v=v; 140 } 141 for(int i=0;i<n;i++){ 142 tmp=abs(point[i].x-s1.x)+abs(point[i].y-s1.y); 143 dis1[i]=tmp; 144 tmp=abs(point[i].x-s2.x)+abs(point[i].y-s2.y); 145 dis2[i]=tmp; 146 } 147 s1_s2=abs(s1.x-s2.x)+abs(s1.y-s2.y); 148 int lown=1,high=inf,ans=-1; 149 while(lown<=high){ 150 int mid=(lown+high)/2; 151 leng=mid; 152 if(slove()){ 153 ans=mid; 154 high=mid-1; 155 } 156 else lown=mid+1; 157 } 158 printf("%d\n",ans); 159 } 160 return 0; 161 }
