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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. // Logic
  48. void solve() {
  49.     int n;
  50.     cin >> n;
  51.     map<int, int> counts;
  52.     rep(i, 0, n) {
  53.         int val;
  54.         cin >> val;
  55.         counts[val]++;
  56.     }
  57.  
  58.     multiset<int> all_pairs;
  59.     vector<int> singles;
  60.     each(p, counts) {
  61.         rep(i, 0, p.ss / 2) {
  62.             all_pairs.insert(p.ff);
  63.         }
  64.         if (p.ss % 2 == 1) {
  65.             singles.pb(p.ff);
  66.         }
  67.     }
  68.     sort(rall(singles));
  69.  
  70.     int max_perimeter = 0;
  71.  
  72.     // Case 0: 0 singles (even sides)
  73.     multiset<int> current_pairs_0 = all_pairs;
  74.     int p_even = 0;
  75.     each(p, current_pairs_0) p_even += p;
  76.     p_even *= 2;
  77.     while (sz(current_pairs_0) >= 2) {
  78.         int s_max = *current_pairs_0.rbegin();
  79.         if (2 * s_max < p_even) {
  80.             max_perimeter = max(max_perimeter, p_even);
  81.             break;
  82.         } else {
  83.             p_even -= 2 * s_max;
  84.             current_pairs_0.erase(prev(current_pairs_0.end()));
  85.         }
  86.     }
  87.  
  88.     // Case 1: 1 single (odd sides)
  89.     multiset<int> current_pairs_1 = all_pairs;
  90.     int p_pairs_1 = 0;
  91.     each(p, current_pairs_1) p_pairs_1 += p;
  92.     p_pairs_1 *= 2;
  93.     while (sz(current_pairs_1) >= 1) {
  94.         int s_pair_max = *current_pairs_1.rbegin();
  95.         bool found = false;
  96.         each(s, singles) {
  97.             int p_total = p_pairs_1 + s;
  98.             int s_max = max(s_pair_max, s);
  99.             if (2 * s_max < p_total) {
  100.                 max_perimeter = max(max_perimeter, p_total);
  101.                 found = true;
  102.                 break;
  103.             }
  104.         }
  105.         if (found) break;
  106.         p_pairs_1 -= 2 * s_pair_max;
  107.         current_pairs_1.erase(prev(current_pairs_1.end()));
  108.     }
  109.  
  110.     // Case 2: 2 singles (even sides)
  111.     if (sz(singles) >= 2) {
  112.         multiset<int> current_pairs_2 = all_pairs;
  113.         int p_pairs_2 = 0;
  114.         each(p, current_pairs_2) p_pairs_2 += p;
  115.         p_pairs_2 *= 2;
  116.         while (sz(current_pairs_2) >= 1) {
  117.             int s_pair_max = *current_pairs_2.rbegin();
  118.             int s1 = singles[0];
  119.             int s2 = singles[1];
  120.             int p_total = p_pairs_2 + s1 + s2;
  121.             int s_max = max(s_pair_max, s1);
  122.             if (2 * s_max < p_total) {
  123.                 max_perimeter = max(max_perimeter, p_total);
  124.                 break;
  125.             } else {
  126.                 p_pairs_2 -= 2 * s_pair_max;
  127.                 current_pairs_2.erase(prev(current_pairs_2.end()));
  128.             }
  129.         }
  130.     }
  131.  
  132.     cout << max_perimeter << endl;
  133. }
  134.  
  135. // Main
  136. int32_t main() {
  137.     fast_io;
  138.  
  139.     int t = 1;
  140.     cin >> t;
  141.     while (t--) {
  142.         solve();
  143.     }
  144.  
  145.     return 0;
  146. }
Success #stdin #stdout 0s 5320KB
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stdout
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https://ideone.com/AeKEth
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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