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 }