This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
//we are all lost trying to be someone.
#include <bits/stdc++.h>
#define fastio ios_base::sync_with_stdio(0); cin.tie(0);
#define sz(x) ll(x.size())
#define reve(x) reverse(x.begin(),x.end())
#define ff first
#define ss second
#define pb push_back
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> ii;
typedef pair<ll, ii >tri;
const ll MAX=3*(1e6+100);
const ll mod=1e9+7;
const ll inf=1e9;
ll A[MAX], pos[MAX];
vector<ii> ans;
ll n;
bool sepuede(){
ll sum=n+1;
for(ll i=1; i<=n/2; i++){
if(A[i]+A[sum-i]!=sum) return false;
}
ll cont=0;
for(ll i=1; i<=n/2; i++){
if(A[i]>n/2)cont++;
}
if(cont%2==1) return false;
return true;
}
void solve(){
cin>>n;
for(ll i=1; i<=n; i++){
cin>>A[i];
}
if(!sepuede()){
cout<<-1<<'\n';
return;
}
for(ll i=1; i<=n/2; i++){
if(A[i]>n/2){
if(A[A[i]]<=n/2 and n-i+1!=A[i]){
ans.push_back({i,A[i]});
ll aux=A[i];
swap(A[i],A[A[i]]);
swap(A[n-i+1],A[n-aux+1]);
}
}
}
ll j=(n/2);
for(ll i=1; i<=n/2; i++){
if(A[i]>n/2){
while(j+1<=n and A[j+1]>n/2) j++;
j++;
ans.push_back({j,i});
ll aux=A[i];
swap(A[i],A[j]);
swap(A[n-i+1],A[n-j+1]);
}
}
for(ll i=1; i<=n/2; i++){
pos[A[i]]=i;
}
ll cont=0;
for(ll i=1; i<=n/2; i++){
if(A[i]!=i){
ll a=pos[i];
ll b=A[i];
ans.pb({a,i});
swap(A[pos[i]],A[i]);
pos[i]=i;
pos[b]=a;
cont++;
}
}
/*
for(ll i=1; i<=n/2; i++){
cout<<A[i]<<" ";
}
cout<<'\n';*/
cout<<sz(ans)<<" "<<sz(ans)<<'\n';
for(ii x:ans){
cout<<x.ff<<" "<<x.ss<<'\n';
}
ans.clear();
return;
}
int main(){
fastio;
ll t;
cin>>t;
while(t--){
solve();
}
return 0;
}
Compilation message (stderr)
cat.cpp: In function 'void solve()':
cat.cpp:57:16: warning: unused variable 'aux' [-Wunused-variable]
57 | ll aux=A[i];
| ^~~
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