codefroces 612E Square Root of Permutation
A permutation of length n is an array containing each integer from 1 to n exactly once. For example, q = [4, 5, 1, 2, 3] is a permutation. For the permutation q the square of permutation is the permutation p that p[i] = q[q[i]] for each i = 1... n. For example, the square of q = [4, 5, 1, 2, 3] is p = q2 = [2, 3, 4, 5, 1].
This problem is about the inverse operation: given the permutation p you task is to find such permutation q that q2 = p. If there are several such q find any of them.
The first line contains integer n (1 ≤ n ≤ 106) — the number of elements in permutation p.
The second line contains n distinct integers p1, p2, ..., pn (1 ≤ pi ≤ n) — the elements of permutation p.
If there is no permutation q such that q2 = p print the number "-1".
If the answer exists print it. The only line should contain n different integers qi (1 ≤ qi ≤ n) — the elements of the permutation q. If there are several solutions print any of them.

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector>
using namespace std;
struct ZYYS
{
int sum;
vector<int>p;
}s[];
int vis[],tot,a[],n,q[],ans[];
bool cmp(ZYYS a,ZYYS b)
{
return a.sum<b.sum;
}
int gi()
{
char ch=getchar();
int x=;
while (ch<''||ch>'') ch=getchar();
while (ch>=''&&ch<='')
{
x=x*+ch-'';
ch=getchar();
}
return x;
}
int dfs(int x,int cnt)
{
if (vis[x]) return cnt;
vis[x]=;
s[tot].p.push_back(x);
dfs(a[x],cnt+);
}
int main()
{int i,flag=,j;
cin>>n;
for (i=;i<=n;i++)
a[i]=gi();
for (i=;i<=n;i++)
if (vis[i]==)
{
s[++tot].sum=dfs(i,);
}
sort(s+,s+tot+,cmp);
for (i=;i<=tot;i++)
{
if (s[i].sum&) continue;
else
{
if (s[i+].sum==s[i].sum) {i++;continue;}
else {flag=;break;}
}
}
if (flag)
{
cout<<-<<endl;
return ;
}
for (i=;i<=tot;i++)
{
if (s[i].sum&)
{
for (j=;j<s[i].sum;j++)
{
q[(*j)%s[i].sum]=s[i].p[j];
}
for (j=;j<s[i].sum;j++)
ans[q[j]]=q[(j+)%s[i].sum];
}
else
{
for (j=;j<s[i].sum;j++)
{
ans[s[i].p[j]]=s[i+].p[j];
ans[s[i+].p[j]]=s[i].p[(j+)%s[i].sum];
}
i++;
}
}
for (i=;i<=n;i++)
printf("%d ",ans[i]);
}
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