题意：给定n个人，每个人指向第a[i]个人，要求输出从每个人开始第一个被访问到两次的人的编号
n<=1e3
思路：
1 #include<cstdio> 2 #include<cstring> 3 #include<string> 4 #include<cmath> 5 #include<iostream> 6 #include<algorithm> 7 #include<map> 8 #include<set> 9 #include<queue> 10 #include<vector> 11 using namespace std; 12 typedef long long ll; 13 typedef unsigned int uint; 14 typedef unsigned long long ull; 15 typedef pair<int,int> PII; 16 typedef vector<int> VI; 17 #define fi first 18 #define se second 19 #define MP make_pair 20 #define N 1100000 21 #define MOD 1000000007 22 #define eps 1e-8 23 #define pi acos(-1) 24 25 int a[N],b[N],n; 26 27 int read() 28 { 29 int v=0,f=1; 30 char c=getchar(); 31 while(c<48||57<c) {if(c=='-') f=-1; c=getchar();} 32 while(48<=c&&c<=57) v=(v<<3)+v+v+c-48,c=getchar(); 33 return v*f; 34 } 35 36 void swap(int &x,int &y) 37 { 38 int t=x;x=y;y=t; 39 } 40 41 int main() 42 { 43 //freopen("1.in","r",stdin); 44 //freopen("1.out","w",stdout); 45 int n; 46 scanf("%d",&n); 47 for(int i=1;i<=n;i++) scanf("%d",&a[i]); 48 for(int i=1;i<=n;i++) 49 { 50 int now=i; 51 for(int j=1;j<=n;j++) b[j]=0; 52 b[now]=1; 53 int flag=0; 54 while(!flag) 55 { 56 now=a[now]; 57 b[now]++; 58 if(b[now]==2) flag=1; 59 } 60 printf("%d ",now); 61 } 62 63 return 0; 64 }