bzoj1529 [POI2005]ska Piggy banks

题目链接

本来是想做强连通分量缩点的题

然而1000000不可搞

于是并查集秒

 1 #include<algorithm>
 2 #include<iostream>
 3 #include<cstdlib>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<string>
 7 #include<cmath>
 8 #include<ctime>
 9 #include<queue>
10 #include<stack>
11 #include<map>
12 #include<set>
13 #define rre(i,r,l) for(int i=(r);i>=(l);i--)
14 #define re(i,l,r) for(int i=(l);i<=(r);i++)
15 #define Clear(a,b) memset(a,b,sizeof(a))
16 #define inout(x) printf("%d",(x))
17 #define douin(x) scanf("%lf",&x)
18 #define strin(x) scanf("%s",(x))
19 #define LLin(x) scanf("%lld",&x)
20 #define op operator
21 #define CSC main
22 typedef unsigned long long ULL;
23 typedef const int cint;
24 typedef long long LL;
25 using namespace std;
26 void inin(int &ret)
27 {
28     ret=0;int f=0;char ch=getchar();
29     while(ch<'0'||ch>'9'){if(ch=='-')f=1;ch=getchar();}
30     while(ch>='0'&&ch<='9')ret*=10,ret+=ch-'0',ch=getchar();
31     ret=f?-ret:ret;
32 }
33 int fa[1000010],n;
34 int find(int x){return x==fa[x]?x:fa[x]=find(fa[x]);}
35 int CSC()
36 {
37     inin(n);re(i,1,n)fa[i]=i;
38     re(i,1,n)
39     {
40         int x;inin(x);
41         int q=find(i),w=find(x);
42         if(q!=w)fa[q]=w;
43     }
44     int ans=0;
45     re(i,1,n)if(fa[i]==i)ans++;
46     printf("%d",ans);
47     return 0;
48 }