Traveling Shopper - FreeCodeCamp #134 Daily Challenge

🛒 Problem Summary

Given an initial amount and a list of items to buy (both in the format ["Amount", "Currency"]), how many can you buy in order, using the following conversion table?

• If you can buy all, return “Buy them all!”
• Otherwise, return “Buy the first x items” (x = number of items you can buy in order).

🔎 Analysis & Strategy

The key is to convert everything to USD before comparing. This avoids errors and simplifies the calculation. The process is:

1. Convert the initial amount to USD.
2. Iterate through the item list, converting each price to USD.
3. Simulate sequential purchases: if you can afford it, subtract; if not, stop and return how many you could buy.

Why not convert to the original currency? Because all rates are given relative to USD, and converting everything to a single currency is more direct and less error-prone.

🧪 Key Test Cases

• The amount is enough for some but not all items → should return the maximum possible.
• The amount is exactly enough for all → “Buy them all!”
• Amount and items in mixed currencies → must convert correctly.
• Less common currencies (JPY, CAD) → robustness.
• Not enough for even the first item → “Buy the first 0 items.”
• Money left after buying everything → still, “Buy them all!”

💡 Commented Implementation

const rates = {
  USD: 1.0,
  EUR: 1.1,
  GBP: 1.25,
  JPY: 0.007,
  CAD: 0.75,
}

export default function buyItems(amount, items) {
  // Convert initial amount to USD
  let budget = Number.parseFloat(amount[0]) * rates[amount[1]]
  let count = 0

  for (const [price, currency] of items) {
    const priceUSD = Number.parseFloat(price) * rates[currency]
    if (budget >= priceUSD) {
      budget -= priceUSD
      count++
    }
    else {
      return `Buy the first ${count} items.`
    }
  }
  return 'Buy them all!'
}

⏱️ Complexity

• Time: $O(n)$ (single pass through the list)
• Space: $O(1)$ (no structures proportional to input)

⚠️ Edge Cases & Tips

• Not enough for even the first item → “Buy the first 0 items.”
• Exactly enough or money left over → “Buy them all!”
• Always convert to USD before comparing.
• Use parseFloat to handle decimals and integers.

🤔 Reflections & Learnings

• Array destructuring.
• Currency conversion with a fixed table.
• Sequential greedy simulation.
• Simple, clear, and optimal code for this case.

📚 Resources

• Exchange rate - Wikipedia
• parseFloat (MDN)
• Greedy Algorithms - GeeksforGeeks