BZOJ1930 [Shoi2003]pacman 吃豆豆

 1 #include<cstdio>
 2 #include<algorithm>
 3 #define N 10010
 4 using namespace std;
 5 int n,i,j,rd[N],t,w,tot,id[N];
 6 int dp,pre[3000000],p[N],tt[3000000],z[N],ID[N],tmp;
 7 int f[2500][2500];
 8 struct g{
 9     int x,y;
10 }a[N];
11 bool cmp(g a,g b)
12 {
13     if (a.x==b.x)
14     return a.y<b.y;
15     return a.x<b.x;
16 }
17 void link(int x,int y)
18 {
19     dp++;pre[dp]=p[x];p[x]=dp;tt[dp]=y;
20 }
21 void Dp(int x,int y)
22 {
23     int i;
24     i=p[x];
25     while (i)
26     {
27             int a=tt[i],b=y;
28             if (id[a]>id[b])
29             swap(a,b);
30             if (a!=b)
31             f[a][b]=max(f[a][b],f[x][y]+1);
32             else
33             f[a][b]=max(f[a][b],f[x][y]);
34         i=pre[i];
35     }
36 }
37 int main()
38 {
39     scanf("%d",&n);
40     
41     for (i=1;i<=n;i++)
42         scanf("%d%d",&a[i].x,&a[i].y);
43     sort(a+1,a+1+n,cmp);
44     for (i=1;i<=n;i++)
45     {
46     tmp=0x37373737*2;
47     for (j=i+1;j<=n;j++)
48     if ((i!=j)&&(a[i].x<=a[j].x)&&(a[i].y<=a[j].y)&&(a[j].y<tmp))
49     {
50         tmp=a[j].y;
51         rd[j]++;
52          link(i,j);
53     }
54     }
55     for (i=1;i<=n;i++)
56     {
57         link(0,i);rd[i]++;
58         link(i,n+1);rd[n+1]++;
59     }
60     t=0;w=1;z[w]=0;
61     while (t!=w)
62     {
63         tot++;
64                 t++;
65         id[z[t]]=tot;
66         ID[tot]=z[t];
67         i=p[z[t]];
68         while (i)
69         {
70             rd[tt[i]]--;
71             if (rd[tt[i]]==0)
72             {
73                 w++;z[w]=tt[i];
74             }
75             i=pre[i];
76         }
77     }
78 
79     
80     for (i=1;i<=tot;i++)
81         for (j=i;j<=tot;j++)
82             Dp(ID[i],ID[j]);
83     printf("%d\n",f[n+1][n+1]-1);
84 }