【动态规划】【缩点】NCPC 2014 G Outing

  1 //
  2 //by coolxxx
  3 //#include<bits/stdc++.h>
  4 #include<iostream>
  5 #include<algorithm>
  6 #include<string>
  7 #include<iomanip>
  8 #include<map>
  9 #include<stack>
 10 #include<queue>
 11 #include<set>
 12 #include<bitset>
 13 #include<memory.h>
 14 #include<time.h>
 15 #include<stdio.h>
 16 #include<stdlib.h>
 17 #include<string.h>
 18 //#include<stdbool.h>
 19 #include<math.h>
 20 #define min(a,b) ((a)<(b)?(a):(b))
 21 #define max(a,b) ((a)>(b)?(a):(b))
 22 #define abs(a) ((a)>0?(a):(-(a)))
 23 #define lowbit(a) (a&(-a))
 24 #define sqr(a) ((a)*(a))
 25 #define swap(a,b) ((a)^=(b),(b)^=(a),(a)^=(b))
 26 #define mem(a,b) memset(a,b,sizeof(a))
 27 #define eps (1e-8)
 28 #define J 10
 29 #define mod 1000000007
 30 #define MAX 0x7f7f7f7f
 31 #define PI 3.14159265358979323
 32 #define N 1004
 33 using namespace std;
 34 typedef long long LL;
 35 int cas,cass;
 36 int n,m,lll,ans;
 37 int fa[N],pre[N],num[N],e[N],t[N],last[N],in[N],q[N];
 38 bool f[N][N];
 39 bool u[N];
 40 struct xxx
 41 {
 42     int next,to;
 43 }a[N];
 44 void cover(int x)
 45 {
 46     int i=e[x];
 47     fa[x]=x;
 48     num[x]=1;
 49     while(i!=x)
 50     {
 51         num[x]++;
 52         num[i]=0;
 53         fa[i]=x;
 54         i=e[i];
 55     }
 56 }
 57 void dfs(int u)
 58 {
 59     if(t[u])
 60     {
 61         if(t[u]>cass)cover(u);
 62         return;
 63     }
 64     t[u]=++cas;
 65     //fa[u]=e[u];
 66     dfs(e[u]);
 67 }
 68 void add(int x,int y)
 69 {
 70     a[++lll].next=last[x];
 71     a[lll].to=y;
 72     last[x]=lll;
 73 }
 74 int work(int now)
 75 {
 76     int i,to,sum=0;
 77     for(i=last[now];i;i=a[i].next)
 78     {
 79         to=a[i].to;
 80         sum+=work(to);
 81     }
 82     return sum+num[now];
 83 }
 84 void spfa()
 85 {
 86     int i,l=0,r=0,now,to;
 87     mem(u,0);cas=0;
 88     for(i=1;i<=n;i++)
 89         if(!in[i] && num[i])q[++cas]=i,pre[i]=work(i);
 90 }
 91 
 92 int main()
 93 {
 94     #ifndef ONLINE_JUDGE
 95 //    freopen("1.txt","r",stdin);
 96 //    freopen("2.txt","w",stdout);
 97     #endif
 98     int i,j,k;
 99     int x,y,z;
100 //    for(scanf("%d",&cass);cass;cass--)
101 //    for(scanf("%d",&cas),cass=1;cass<=cas;cass++)
102 //    while(~scanf("%s",s+1))
103     while(~scanf("%d",&n))
104     {
105         lll=0;mem(num,0);mem(t,0);mem(in,0);mem(last,0);mem(pre,0);mem(f,0);
106         scanf("%d",&m);
107         for(i=1;i<=n;i++)
108         {
109             scanf("%d",&e[i]);
110             num[i]=1;fa[i]=i;
111         }
112         cas=0;
113         for(i=1;i<=n;i++)
114         {
115             if(t[i])continue;
116             cass=cas;
117             dfs(i);
118         }
119         for(i=1;i<=n;i++)
120         {
121             if(num[i]==0 || fa[e[i]]==i)continue;
122             add(fa[e[i]],i);
123             in[i]++;
124         }
125         spfa();
126         f[0][0]=1;
127         for(i=1;i<=cas;i++)
128         {
129             x=q[i];y=q[i-1];
130             for(j=0;j<=m;j++)
131             {
132                 f[x][j]|=f[y][j];
133                 for(k=num[x];k<=pre[x] && j+k<=m;k++)
134                     f[x][j+k]|=f[y][j];
135             }
136         }
137         x=q[cas];
138         for(i=m;i;i--)
139             if(f[x][i])break;
140         printf("%d\n",i);
141     }
142     return 0;
143 }
144 /*
145 //
146 
147 //
148 */