bzoj1340: [Baltic2007]Escape逃跑问题

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define rep(i,l,r) for(int i=l;i<=r;++i)
 4 const int N=202333,inf=2147483647;
 5 int head[N],n,m,dis[N],tot=1,sum,T,K;
 6 struct node{
 7     int x,y;
 8 }s[N];
 9 struct zs{
10     int to,next,w;
11 }e[N];
12 inline void ins(int u,int v,int w){
13     e[++tot].to=v; e[tot].next=head[u]; head[u]=tot; e[tot].w=w;
14 }
15 inline void insert(int u,int v,int w){
16     ins(u,v,w); ins(v,u,0);
17 }
18 inline bool bfs(){
19      rep(i,0,T) dis[i]=-1; queue<int>q; q.push(0); dis[0]=0;
20      while(!q.empty()) {
21           int x=q.front(); q.pop();
22           for(int k=head[x];k;k=e[k].next) 
23              if(dis[e[k].to]<0 && e[k].w>0) {
24                    dis[e[k].to]=dis[x]+1; q.push(e[k].to);
25              }
26      }
27      if(dis[T]>0) return 1;else return 0;
28 }
29 int find(int x,int low){
30      if(x==T) return low;
31      int delta=low,now;
32      for(int k=head[x];k;k=e[k].next) 
33        if(e[k].w>0 && dis[e[k].to]==dis[x]+1){ 
34            now=find(e[k].to,min(e[k].w,delta));
35            e[k].w-=now; e[k^1].w+=now;   delta-=now;
36            if(!delta) return low;
37         } 
38      dis[x]=-1;
39      return low-delta;
40 }
41 int main(){
42     scanf("%d%d%d",&n,&m,&K);
43     T=K*2+1;
44     rep(i,1,K) {
45         scanf("%d%d",&s[i].x,&s[i].y);
46         if(s[i].y<=100) insert(0,i,inf);
47         if(abs(s[i].y-m)<=100) insert(i+K,T,inf);
48         insert(i,i+K,1);
49     }
50     rep(i,1,K) rep(j,1,K) if(i!=j&&(s[i].x-s[j].x)*(s[i].x-s[j].x)+(s[i].y-s[j].y)*(s[i].y-s[j].y)<=200*200)
51                             insert(i+K,j,inf);
52     while(bfs()) sum+=find(0,inf);
53     printf("%d\n",sum);
54 }