Pair sort

input/code.cpp: In function 'int solve()':
input/code.cpp:150:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  150 |     for (int i = 0; i < res.size(); i++) {
      |                     ~~^~~~~~~~~~~~

#ifdef ONPC
    #define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>

#define char unsigned char
#define rep(i, a, b) for(int i=a; i< (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define pb push_back

#define LSOne(S) ((S) & -(S))

using namespace std;
// mt19937 rnd(239);
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

typedef long long C;
typedef complex<C> P;
#define X real()
#define Y imag()

template<class T>
istream& operator>> (istream& is, complex<T>& p) {
    T value;
    is >> value;
    p.real(value);
    is >> value;
    p.imag(value);
    return is;
}

typedef long long ll;
typedef long double ld;

using pi = pair<ll, ll>;
using vi = vector<ll>;
template <class T>
using pq = priority_queue<T>;
template <class T>
using pqg = priority_queue<T, vector<T>, greater<T>>;

int popcnt(int x) { return __builtin_popcount(x); }
int popcnt(ll x) { return __builtin_popcountll(x); }

#define MIN(v) *min_element(all(v))
#define MAX(v) *max_element(all(v))
#define LB(c, x) distance((c).begin(), lower_bound(all(c), (x)))
#define UB(c, x) distance((c).begin(), upper_bound(all(c), (x)))

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef DEBUG
#define dbg(x...) cerr << "\e[91m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << endl;
#else
#define dbg(x...)
#endif

template<typename S, typename T = S> void chmin(S &s, T t) {s = s < t ? s : t;}
template<typename S, typename T = S> void chmax(S &s, T t) {s = s > t ? s : t;}

const int INF = 1e9; // 10^9 = 1B is < 2^31-1
const ll LLINF = 4e18; // 4*10^18 is < 2^63-1
const double EPS = 1e-9;
const ll MOD = 1e9+7;

int solve() {
    int n; std::cin >> n;
    vector<int> v(2*n);
    std::set<int> used;
    std::map<int, vector<int>> pos;
    
    for (int i = 0; i < 2*n; i++) {
        std::cin >> v[i];
        pos[v[i]].pb(i);
    }


    std::map<int, int> badPos;
    std::map<int, int> goodPos;
    vector<int> toCorr(n);
    vector<int> toCorrPos(n);

    std::vector<int> inBadPos;

    for (int i = 0; i < 2*n; i+=2) {
        if(v[i]==v[i+1]) {
            toCorr[i/2]=v[i];
            continue;
        }
        if(!used.count(v[i])) {
            goodPos[v[i]]=i;
            badPos[v[i+1]]=i+1;

            
            inBadPos.pb(v[i+1]);
            toCorr[i/2]=v[i];
            toCorrPos[i/2]=i+1;
            used.insert(v[i]);
        } else if(!used.count(v[i+1])) {
            goodPos[v[i+1]]=i+1;
            badPos[v[i]]=i;

            inBadPos.pb(v[i]);
            toCorr[i/2]=v[i+1];
            toCorrPos[i/2]=i;
            used.insert(v[i+1]);
        } 
    }
    if(false) {
    __print(inBadPos); std::cout  << std::endl;

    __print(toCorr); std::cout  << std::endl;

    __print(goodPos); std::cout  << std::endl;
    __print(badPos); std::cout  << std::endl;
    }
    vector<pair<int,int>> res;
    for (int i = 1; i < n; i++) {
        int a=badPos[inBadPos[i]],b=badPos[inBadPos[i-1]];
        res.pb({a+1, b+1});
        swap(v[a],v[b]);
    }
    
    std::cout << res.size() << std::endl;
    for (int i = 0; i < res.size(); i++) {
        std::cout << res[i].fi << " " << res[i].se << endl;
    }

    //__print(v); std::cout  << std::endl;

    return 0;



    for(auto &w:pos) {
        std::cout << w.fi << ": ";
        __print(w.se); std::cout  << std::endl;
    }
    __print(toCorr); std::cout  << std::endl;
    __print(toCorrPos); std::cout  << std::endl;
    for (int i = 0; i < n; i+=2) {
        //if(v[i]==toCorr[i/2] && v[i+1]==toCorr[i/2]) continue;
        if(v[i]!=toCorr[i/2]) {
            
        }
        if(v[i+1]!=toCorr[i/2]) {
            
        }

    }
    


    return 0;
}

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int TET = 1;
    //cin >> TET;
    for (int i = 1; i <= TET; i++) {
        #ifdef ONPC
            cout << "TEST CASE#" << i << endl;
        #endif
        
        if (solve()) {
            break;
        }

        #ifdef ONPC
            cout << "__________________________" << endl;
        #endif
    }
    #ifdef ONPC
        cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
    #endif
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: WRONG ANSWER