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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. // Speed
  5. #define fast_io ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
  6.  
  7. // Typedefs
  8. #define int long long
  9. #define pb push_back
  10. #define ff first
  11. #define ss second
  12. #define all(x) (x).begin(), (x).end()
  13. #define rall(x) (x).rbegin(), (x).rend()
  14. #define sz(x) ((int)(x).size())
  15. #define endl '\n'
  16. #define yes cout << "yes\n"
  17. #define no cout << "no\n"
  18.  
  19. // Loops
  20. #define rep(i,a,b) for(int i=a;i<b;++i)
  21. #define per(i,a,b) for(int i=b-1;i>=a;--i)
  22. #define each(x, a) for (auto& x : a)
  23.  
  24. // Consts
  25. const int INF = 1e18;
  26. const int MOD = 1e9+7;
  27. const int N = 2e5 + 5;
  28.  
  29. // Math
  30. int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
  31. int lcm(int a, int b) { return (a / gcd(a, b)) * b; }
  32.  
  33. int power(int a, int b, int m = MOD) {
  34.     int res = 1;
  35.     while (b > 0) {
  36.         if (b & 1) res = res * a % m;
  37.         a = a * a % m;
  38.         b >>= 1;
  39.     }
  40.     return res;
  41. }
  42.  
  43. int modinv(int a, int m = MOD) {
  44.     return power(a, m - 2, m);
  45. }
  46.  
  47. void count_inversions(vector<int>& a, int& inv) {
  48.     int n = a.size();
  49.     vector<int> temp(n);
  50.  
  51.     function<void(int, int)> merge_sort = [&](int l, int r) {
  52.         if (r - l <= 1) return;
  53.         int m = (l + r) / 2;
  54.         merge_sort(l, m);
  55.         merge_sort(m, r);
  56.  
  57.         int i = l, j = m, k = l;
  58.         while (i < m && j < r) {
  59.             if (a[i] <= a[j]) temp[k++] = a[i++];
  60.             else {
  61.                 temp[k++] = a[j++];
  62.                 inv += m - i;
  63.             }
  64.         }
  65.         while (i < m) temp[k++] = a[i++];
  66.         while (j < r) temp[k++] = a[j++];
  67.         rep(x, l, r) a[x] = temp[x];
  68.     };
  69.  
  70.     merge_sort(0, n);
  71. }
  72.  
  73. void solve() {
  74.     int n;
  75.     cin >> n;
  76.     vector<int> p(n);
  77.     rep(i, 0, n) cin >> p[i];
  78.  
  79.     int minInv = INF;
  80.     vector<int> a(n);
  81.  
  82.     for (int mask = 0; mask < (1 << n); ++mask) {
  83.         rep(i, 0, n)
  84.             a[i] = (mask >> i & 1) ? (2 * n - p[i]) : p[i];
  85.  
  86.         int inv = 0;
  87.         count_inversions(a, inv);
  88.         minInv = min(minInv, inv);
  89.     }
  90.  
  91.     cout << minInv << endl;
  92. }
  93.  
  94. // Main
  95. int32_t main() {
  96.     fast_io;
  97.  
  98.     int t;
  99.     cin >> t;
  100.     while (t--) {
  101.         solve();
  102.     }
  103.  
  104.     return 0;
  105. }
Success #stdin #stdout 0.01s 5320KB
comments (?)
stdin 
5
2
2 1
3
2 1 3
4
4 3 2 1
5
2 3 1 5 4
6
2 3 4 1 5 6
stdout 
0
1
0
2
2
https://ideone.com/AgzQvH
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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