Optimal sort

input/code.cpp: In function 'int main()':
input/code.cpp:23:40: warning: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'll' {aka 'long long int'} [-Wsign-compare]
   23 | #define fr(i,a,b) for (size_t i = a; i < b; i++)
      |                                        ^
input/code.cpp:50:3: note: in expansion of macro 'fr'
   50 |   fr(i, 0, n) { rev_idx[a[i]] = i; }
      |   ^~
input/code.cpp:23:40: warning: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'll' {aka 'long long int'} [-Wsign-compare]
   23 | #define fr(i,a,b) for (size_t i = a; i < b; i++)
      |                                        ^
input/code.cpp:53:3: note: in expansion of macro 'fr'
   53 |   fr(i, 0, n) {
      |   ^~

// clang-format off
#include <bits/stdc++.h>
#include <unordered_map>
using namespace std;
#ifdef DO_DBG
template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cerr << ' ' << H; dbg_out(T...); }
#define dbg(...) cerr << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#define dout cerr
#define debug true
#else
#define dbg(...)
#define dout if (0) cerr
#define debug false
#endif
typedef long long ll; typedef unsigned long long ull; typedef long double ld;
template <typename T> using v = vector<T>; template <typename T> using us = unordered_set<T>; template <typename K, typename V> using p = pair<K,V>;
template <typename K, typename V> using um = unordered_map<K, V>; template <typename K, typename V> using p = pair<K, V>;
template <typename T> using pq = priority_queue<T>; template <typename T> using nl = numeric_limits<T>; template <typename T> using il = initializer_list<T>;
constexpr int MOD = 1e9 + 7; constexpr int INF = 1e9; constexpr ld EPS = 1e-9;
#define fr(i,a,b) for (size_t i = a; i < b; i++)
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); cin.exceptions(cin.failbit);
#define frr(i,a,b) for (size_t i = b-1; i >= a; i--)
#define frs(i,a,b) for (ll i = a; i < b; i++)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define sq(x) ((x) * (x))
template <typename... Args> void read(Args&... args) { ((cin >> args), ...); }
#define d(...) int __VA_ARGS__; read(__VA_ARGS__);
#define dll(...) ll __VA_ARGS__; read(__VA_ARGS__);
#define dv(x, n) vector<int> x(n); for (int i = 0; i < n; i++) cin >> x[i];
#define dvll(x, n) vector<long long> x(n); for (int i = 0; i < n; i++) cin >> x[i];
#define dvd(x, n) vector<double> x(n); for (int i = 0; i < n; i++) cin >> x[i];
ll ipow(ll a,int b){ll r=1;for(;b;b>>=1,a*=a)if(b&1)r*=a;return r;}
template<class F>struct y_combinator{F f;template<class...Args>decltype(auto)operator()(Args&&...args)const{return f(*this,forward<Args>(args)...);}};
constexpr auto get_nums=[]<typename T>(T&&s){istringstream iss(forward<T>(s));return vector<int>{istream_iterator<int>{iss},{}};};
// clang-format on

int main() {
  fastio;
  dll(n);
  dvll(a, n);
  v<ll> sa(a); // sort array and keep index

  // fr(i, 0, n) { sa[i] = {a[i], i}; }
  sort(all(sa));
  unordered_map<ll, ll> rev_idx;
  fr(i, 0, n) { rev_idx[a[i]] = i; }

  ll ops = 0;
  fr(i, 0, n) {
    if (a[i] != sa[i]) {
      ops++;
      auto sai_idx = rev_idx[sa[i]];
      // we need to swap a[sai_idx] and a[i]
      rev_idx[a[i]] = sai_idx;
      rev_idx[sa[i]] = i;
      a[sai_idx] = a[i];
      // sai_idx = a.index(sa[i])
      // a[sai_idx] = a[i]
      // a[i] = sa[i]
    }
    dbg(a);
  }
  cout << ops << '\n';
}

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

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: ACCEPTED

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: ACCEPTED

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: ACCEPTED

Test 51

Verdict: ACCEPTED

Test 52

Verdict: ACCEPTED

Test 53

Verdict: ACCEPTED

Test 54

Verdict: ACCEPTED

Test 55

Verdict: ACCEPTED

Test 56

Verdict: ACCEPTED

Test 57

Verdict: ACCEPTED

Test 58

Verdict: ACCEPTED

Test 59

Verdict: ACCEPTED

Test 60

Verdict: ACCEPTED

Test 61

Verdict: ACCEPTED

Test 62

Verdict: ACCEPTED

Test 63

Verdict: ACCEPTED

Test 64

Verdict: ACCEPTED

Test 65

Verdict: ACCEPTED

Test 66

Verdict: ACCEPTED

Test 67

Verdict: ACCEPTED

Test 68

Verdict: ACCEPTED

Test 69

Verdict: ACCEPTED

Test 70

Verdict: ACCEPTED