[bzoj1930] [Shoi2003]pacman 吃豆豆

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cmath>
 6 #define ll long long
 7 using namespace std;
 8 const int maxn=4023,inf=1002333333;
 9 struct poi{int x,y;}a[maxn];
10 struct zs{int pre;short too,flow,dis;}e[4233333];int tot,last[maxn];
11 short dl[4233333];
12 int dis[maxn];
13 bool u[maxn],ins[maxn];
14 int i,j,k,n,m,s,t,ss;
15 int ans;
16 
17 int ra;char rx;
18 inline int read(){
19     rx=getchar(),ra=0;
20     while(rx<‘0‘||rx>‘9‘)rx=getchar();
21     while(rx>=‘0‘&&rx<=‘9‘)ra*=10,ra+=rx-48,rx=getchar();return ra;
22 }
23 
24 bool spfa(){
25     memset(dis,255,(t+1)<<2),dis[ss]=0,dl[1]=ss,u[ss]=1;
26     int l=0,r=1,i,now;
27     while(l<r&&!dis[ss])
28         for(i=last[now=dl[++l]],u[now]=0;i;i=e[i].pre)if(e[i].flow&&dis[e[i].too]<dis[now]+e[i].dis){
29             dis[e[i].too]=dis[now]+e[i].dis;
30             if(!u[e[i].too])u[e[i].too]=1,dl[++r]=e[i].too;
31         }
32     return dis[t]>-1;
33 }
34 inline int min(int a,int b){return a<b?a:b;}
35 int dfs(int x,int mx){
36     if(x==t)return mx;
37     int used=0,i,w;ins[x]=1;
38     for(i=last[x];i;i=e[i].pre)if(e[i].flow&&dis[e[i].too]==dis[x]+e[i].dis&&!ins[e[i].too])
39         if((w=dfs(e[i].too,min(mx-used,(int)e[i].flow)))){
40             e[i].flow-=w,e[i^1].flow+=w,ans+=w*e[i].dis,used+=w;
41             if(used==mx){ins[x]=0;return mx;}
42         }
43     dis[x]=-1,ins[x]=0;return used;
44 }
45 
46 inline void insert(int a,int b,int c,int d){
47     e[++tot].too=b,e[tot].flow=c,e[tot].dis= d,e[tot].pre=last[a],last[a]=tot,
48     e[++tot].too=a,e[tot].flow=0,e[tot].dis=-d,e[tot].pre=last[b],last[b]=tot;
49 }
50 bool cmp(poi a,poi b){return a.x<b.x||(a.x==b.x&&a.y<b.y);}
51 int main(){
52     n=read();
53     for(i=1;i<=n;i++)
54         a[i].x=read(),a[i].y=read();
55     sort(a+1,a+1+n,cmp);
56     ss=0,s=n<<1|1,t=s+1,tot=1;
57     insert(ss,s,2,0);
58     for(i=1;i<=n;i++){
59         insert(i,i+n,1,0),insert(i,i+n,1,1),insert(s,i,1,0),insert(i+n,t,1,0);
60         int mn=inf;
61         for(j=i+1;j<=n;j++)
62             if(a[j].y<mn&&a[j].y>=a[i].y)mn=a[j].y,insert(i+n,j,2,0);
63     }
64     while(spfa())dfs(ss,inf);
65     printf("%d\n",ans);
66 }