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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. int count_inversions(vector<int> a) {
  48.     int inv = 0;
  49.     int n = a.size();
  50.     vector<int> temp(n);
  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.         int i = l, j = m, k = l;
  57.         while (i < m && j < r) {
  58.             if (a[i] <= a[j]) temp[k++] = a[i++];
  59.             else {
  60.                 inv += m - i;
  61.                 temp[k++] = a[j++];
  62.             }
  63.         }
  64.         while (i < m) temp[k++] = a[i++];
  65.         while (j < r) temp[k++] = a[j++];
  66.         rep(i, l, r) a[i] = temp[i];
  67.     };
  68.     merge_sort(0, n);
  69.     return inv;
  70. }
  71.  
  72. // Logic
  73. void solve() {
  74.     // Code
  75.     int n;
  76.     cin >> n;
  77.     vector<int> p(n);
  78.     rep(i, 0, n) cin >> p[i];
  79.  
  80.     int minInv = INF;
  81.     vector<int> a(n);
  82.  
  83.     for (int mask = 0; mask < (1 << n); ++mask) {
  84.         rep(i, 0, n) {
  85.             if ((mask >> i) & 1)
  86.                 a[i] = 2 * n - p[i];
  87.             else
  88.                 a[i] = p[i];
  89.         }
  90.         minInv = min(minInv, count_inversions(a));
  91.     }
  92.  
  93.     cout << minInv << endl;
  94. }
  95.  
  96. // Main
  97. int32_t main() {
  98.     fast_io;
  99.  
  100.     int t;
  101.     cin >> t;
  102.     while (t--) {
  103.         solve();
  104.     }
  105.  
  106.     return 0;
  107. }
Success #stdin #stdout 0s 5316KB
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5
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2 1
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4 3 2 1
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stdout
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https://ideone.com/6kYX7G
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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