【BZOJ】【1529】 【POI2005】ska Piggy banks

 1 /**************************************************************
 2     Problem: 1529
 3     User: Tunix
 4     Language: C++
 5     Result: Memory_Limit_Exceed
 6 ****************************************************************/
 7  
 8 //BZOJ 1529
 9 #include<cstdio>
10 #include<cstring>
11 #include<cstdlib>
12 #include<iostream>
13 #include<algorithm>
14 #define rep(i,n) for(int i=0;i<n;++i)
15 #define F(i,j,n) for(int i=j;i<=n;++i)
16 #define D(i,j,n) for(int i=j;i>=n;--i)
17 using namespace std;
18 const int N=1000086;
19  
20 void read(int &v){
21     v=0;int sign=1; char ch=getchar();
22     while(ch<‘0‘ || ch>‘9‘) {if (ch==‘-‘) sign=-1; ch=getchar();}
23     while(ch>=‘0‘&&ch<=‘9‘){v=v*10+ch-‘0‘; ch=getchar();}
24     v*=sign;
25 }
26 /********************tamplate*******************/
27 int dfn[N],low[N],dfs_clock,SCC=0,belong[N],n;
28 int head[N],to[N],next[N],cnt;
29 void ins(int x,int y){
30     to[++cnt]=y; next[cnt]=head[x]; head[x]=cnt;
31 }
32 int t[N],ne[N],h[N];
33 void add(int x,int y){
34     t[++cnt]=y; ne[cnt]=h[x]; h[x]=cnt;
35 }
36 bool inst[N];
37 int st[N],top=0;
38 void tarjan(int x){
39     int y;
40     dfn[x]=low[x]=++dfs_clock;
41     st[top++]=x;
42     inst[x]=1;
43     for(int i=head[x];i;i=next[i]){
44         y=to[i];
45         if (!dfn[y]){
46             tarjan(y);
47             low[x]=min(low[x],low[y]);
48         }
49         else if (inst[y]) low[x]=min(low[x],dfn[y]);
50     }
51     if (dfn[x]==low[x]){
52         ++SCC;
53         for(y=0;y!=x;){
54             y=st[--top];
55             inst[y]=0;
56             belong[y]=SCC;
57         }
58     }
59 }
60 int in[N];
61 void rebuild(){
62     F(x,1,n)
63         for(int i=head[x];i;i=next[i])
64             if (belong[x]!=belong[to[i]]){
65                 add(belong[x],belong[to[i]]);
66                 in[belong[to[i]]]++;
67             }
68 }
69 /***********************************************/
70  
71 int main(){
72 #ifndef ONLINE_JUDGE
73     freopen("1529.in","r",stdin);
74 #endif
75     read(n);
76     int x;
77     F(i,1,n){
78         read(x);
79         ins(x,i);
80     }
81     F(i,1,n) if (!dfn[i]) tarjan(i);
82     rebuild();
83     int ans=0;
84     F(i,1,SCC) if(in[i]==0) ans++;
85     printf("%d\n",ans);
86     return 0;
87 }

 1 /**************************************************************
 2     Problem: 1529
 3     User: Tunix
 4     Language: C++
 5     Result: Accepted
 6     Time:908 ms
 7     Memory:4712 kb
 8 ****************************************************************/
 9  
10 //BZOJ 1529
11 #include<cstdio>
12 #define rep(i,n) for(int i=0;i<n;++i)
13 #define F(i,j,n) for(int i=j;i<=n;++i)
14 #define D(i,j,n) for(int i=j;i>=n;--i)
15 using namespace std;
16 const int N=1000086;
17  
18 void read(int &v){
19     v=0;int sign=1; char ch=getchar();
20     while(ch<‘0‘ || ch>‘9‘) {if (ch==‘-‘) sign=-1; ch=getchar();}
21     while(ch>=‘0‘&&ch<=‘9‘){v=v*10+ch-‘0‘; ch=getchar();}
22     v*=sign;
23 }
24 int fa[N],n;
25 int getfather(int x){
26     if (fa[x]!=x) fa[x]=getfather(fa[x]);
27     return fa[x];
28 }
29 int main(){
30     read(n);
31     int x;
32     F(i,1,n) fa[i]=i;
33     F(i,1,n){
34         read(x);
35         int f1=getfather(i),f2=getfather(x);
36         if (f1!=f2) fa[f1]=f2;
37     }
38     int ans=0;
39     F(i,1,n) if (fa[i]==i) ans++;
40     printf("%d\n",ans);
41     return 0;
42 }