Problem Description

Implement the core purchase logic for a gem-based card game. Players collect gems to buy cards, and these cards provide permanent discounts on future purchases of specific gem colors.

Entities

• Gem Colors: There are five distinct gem colors: BLUE, WHITE, GREEN, RED, and YELLOW.
• Card:
  • color: Represents the gem color for which this card provides a permanent discount once purchased.
  • cost: A map where keys are gem colors and values are the quantities of those gems required to purchase the card.
• Player:
  • gems: A map representing the player's current inventory of gems, mapping gem colors to their respective quantities.
  • hand: A collection (e.g., list or set) of Card objects the player has successfully purchased.
  • discountMap: A map tracking the total discounts a player receives for each gem color. discountMap[c] indicates the number of previously purchased cards of color c, which directly translates to the discount applied for that gem color.

Rules for Purchasing

1. Discount Application: When a player attempts to buy a card, a discount is applied to each gem color required for the card's cost. The discount for a specific gem color is equal to the number of cards of that same color the player already owns (as tracked in discountMap).
   • Example: If a player owns 2 white cards and 1 red card, and attempts to buy a card costing 4 white gems and 1 red gem, the discounted cost would be 2 white gems (4 - 2) and 0 red gems (1 - 1).
2. Minimum Discounted Cost: The discounted cost for any gem color cannot fall below zero. If the discount exceeds the required quantity for a gem, the cost for that gem becomes 0.

Required Functions

You must implement the following two functions:

1. canPurchase(card):
   • This function should return true if the player can afford the given card after applying all relevant discounts, and false otherwise. It should not modify the player's state.
2. purchase(card):
   • If the card is not affordable (as determined by canPurchase), this function should return false and ensure no changes are made to the player's state.
   • If the card is affordable, this function must:
     • Deduct the calculated discounted gem cost from the player's gems inventory.
     • Add the card to the player's hand.
     • Increment the discount count for the purchased card's color in the player's discountMap by 1.
     • Return true.