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  1. #include <iostream>
  2. #include <vector>
  3. #include <unordered_map>
  4.  
  5. int max_coins(const std::vector<int>& deck, int n, int k) {
  6.     // Create a frequency map of card types
  7.     std::unordered_map<int, int> card_count;
  8.     for (int i = 0; i < n; i++) {
  9.         card_count[deck[i]]++;
  10.     }
  11.  
  12.     int coins = 0;
  13.  
  14.     // Create the initial hand with the first k cards
  15.     std::unordered_map<int, int> hand;
  16.     for (int i = 0; i < k; i++) {
  17.         hand[deck[i]]++;
  18.         card_count[deck[i]]--;
  19.     }
  20.  
  21.     // Function to count pairs in the given map
  22.     auto count_pairs = [](std::unordered_map<int, int>& map) {
  23.         int pairs = 0;
  24.         for (auto& entry : map) {
  25.             pairs += entry.second / 2; // Count how many pairs can be made
  26.         }
  27.         return pairs;
  28.     };
  29.  
  30.     coins += count_pairs(hand); // Start by counting pairs in the initial hand
  31.  
  32.     int deck_index = k; // Points to the next card in the deck
  33.     while (deck_index < n) {
  34.         // Two new cards are drawn from the deck
  35.         hand[deck[deck_index]]++;
  36.         hand[deck[deck_index + 1]]++;
  37.         deck_index += 2; // Increment by two as two cards are drawn
  38.  
  39.         // Check for pairs in the hand
  40.         coins += count_pairs(hand);
  41.  
  42.         // Remove pairs from the hand
  43.         for (auto it = hand.begin(); it != hand.end();) {
  44.             if (it->second >= 2) {
  45.                 it->second %= 2; // Keep only the remainder if there were pairs
  46.             }
  47.             if (it->second == 0) {
  48.                 it = hand.erase(it); // Remove card type from the hand if there are no cards left
  49.             } else {
  50.                 it++;
  51.             }
  52.         }
  53.     }
  54.  
  55.     return coins;
  56. }
  57.  
  58. int main() {
  59.     int n, k;
  60.     std::cin >> n >> k;
  61.  
  62.     std::vector<int> deck(n);
  63.     for (int i = 0; i < n; i++) {
  64.         std::cin >> deck[i];
  65.     }
  66.  
  67.     std::cout << max_coins(deck, n, k) << std::endl;
  68.     return 0;
  69. }
  70.  
Success #stdin #stdout 0.01s 5272KB
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https://ideone.com/dusrgF
language:
C++14 (gcc 8.3)
created:
17 days ago
visibility:
public

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