Pair sort

#include<bits/stdc++.h>
//#include<unordered_set>
#pragma GCC optimize("Ofast")
using namespace std;
#define int long long
#define die(x) return cout << x << endl, 0
#define FI first
#define SE second
#define all(o) o.begin(), o.end()
#define endl '\n'
#define IOS ios::sync_with_stdio(0), cin.tie(0)
#define FILE freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout)
#define SZ(x) ((int)(x).size())
#define PB push_back
#define PF push_front
#define POB pop_back
#define POF pop_front
#define MP make_pair
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef map<int,int> mpi;
typedef set<int> sti;
typedef vector<pii> vii;
typedef map<pii,int> mpii;
typedef set<pii> stii;
typedef long double ld;
typedef long long ll;
int gcd(int x,int y){ return (!y ? x : gcd(y, x%y)); }
int power(int x, int y) { return (!y ? 1 : power(x, y / 2) * power(x, y / 2) * (y % 2 ? x : 1)); }
int to_int(string sconvert){stringstream geek(sconvert);int xconvert = 0; geek >> xconvert; return xconvert;}
int fastMax(int x, int y) { return (((y-x)>>(32-1))&(x^y))^y; }
int fastMin(int x, int y) { return (((y-x)>>(32-1))&(x^y))^x; }
const int MAXN=2e5+30,MAX_LOG=30,MOD=1e9+7,INF=1e9;
const double PI = acos(-1);
int mod(int x) { return (x % MOD + MOD) % MOD; }
int n, q;
// int s[MAXN*4+1],lazy[4*MAXN+1],rq[MAXN*4+1];
// int a[MAXN],ans[MAXN];
// void build(int id=1,int l=0,int r=n){
//     if(r-l<2){
//         s[id]=a[l];
//         rq[id]=a[l];
//         return;
//     }
//     int mid=(l+r)/2;
//     build(id*2,l,mid);build(id*2+1,mid,r);
//     s[id]=s[id*2]+s[id*2+1];
//     rq[id]=min(rq[id*2],rq[id*2+1]);
// }
// void upd(int id,int l,int r,int x){
//     lazy[id]+=x;
//     rq[id]+=x;
//     s[id]+=(r-l)*x;
// }
// void shift(int id,int l,int r){
//     int mid=(l+r)/2;
//     upd(id*2,l,mid,lazy[id]);
//     upd(id*2+1,mid,r,lazy[id]);
//     lazy[id]=0;
// }
// void add(int x,int y,int v,int id=1,int l=0,int r=n){
//     if(x>=r || l>=y)return;
//     if(x<=l && r<=y){
//         upd(id,l,r,v);
//         return;
//     }
//     shift(id,l,r);
//     int mid=(l+r)/2;
//     add(x,y,v,id*2,l,mid);
//     add(x,y,v,id*2+1,mid,r);
//     s[id]=s[id*2]+s[id*2+1];
//     rq[id]=min(rq[id*2],rq[id*2+1]);
// }
// int sum(int x,int y,int id=1,int l=0,int r=n){
//     if(x>=r || l>=y)return 0;
//     if(x<=l && r<=y)return s[id];
//     shift(id,l,r);
//     int mid=(l+r)/2;
//     return sum(x,y,id*2,l,mid)+sum(x,y,id*2+1,mid,r);
// }
// int rmq(int x,int y,int id=1,int l=0,int r=n){
//     if(x>=r || l>=y)return INF*INF;
//     if(x<=l && r<=y)return rq[id];
//     shift(id,l,r);
//     int mid=(l+r)/2;
//     return min(rmq(x,y,id*2,l,mid),rmq(x,y,id*2+1,mid,r));
// }

int a[MAXN];
int first_pos[MAXN], second_pos[MAXN];
int MAIN(){
    cin>>n;
    for (int i = 0; i < 2*n; i++){
        cin>>a[i];
        if (first_pos[a[i]] == 0) first_pos[a[i]] = i + 1;
        else second_pos[a[i]] = i + 1;
    }

    vector<pii> swaps;
    for (int i = 0; i < 2*n; i += 2){
        int val = a[i];
        int match_p = first_pos[val] == i + 1 ? second_pos[val] : first_pos[val];
        if (match_p == i+2) continue;

        int ov = a[i+1];
        swaps.push_back({i + 2, match_p});
        a[i + 1] = a[i];
        a[match_p - 1] = ov;

        if (first_pos[val] == match_p) first_pos[val] = i + 2;
        else second_pos[val] = i + 2;
        if (first_pos[ov] == i + 2) first_pos[ov] = match_p;
        else second_pos[ov] = match_p;
    }

    cout<<swaps.size()<<endl;
    for (int i = 0; i <(int)swaps.size(); i++){
        cout<<swaps[i].first<<' '<<swaps[i].second<<endl;
    }

    return 0;
}
int32_t main(){
    IOS;
    int t=1;
    //cin>>t;
    while(t--)MAIN();
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED