Ramiro N. Cosa

Inventory Update - FreeCodeCamp #124 Daily Challenge

3 min

Inventory Update - Analysis and Explanation

Problem Statement

You are given two 2D arrays:

  • The first represents your store’s current inventory.
  • The second, a new shipment of products.

Each element has the format [quantity, product name].

Goal: Update the inventory by adding quantities for existing products and appending new products at the end, preserving the original order.

For example:

// Initial inventory
[[2, 'apples'], [5, 'bananas']]
// New shipment
  [[1, 'apples'], [3, 'bananas']]
// Updated inventory
  [[3, 'apples'], [8, 'bananas']]

Initial Analysis

What does the challenge ask?

Update the store’s inventory after a new shipment, summing quantities for existing products and adding new ones at the end, without losing the original order.

Key Test Cases

These are the most important scenarios:

  1. Update existing products:
    • Inventory and shipment have the same products. Quantities are summed.
    • Example: [[2, "apples"], [5, "bananas"]] and [[1, "apples"], [3, "bananas"]] → [[3, "apples"], [8, "bananas"]].
  2. Add new products:
    • Shipment brings products not present in inventory. They are added at the end.
    • Example: [[2, "apples"], [5, "bananas"]] and [[1, "apples"], [3, "bananas"], [4, "oranges"]] → [[3, "apples"], [8, "bananas"], [4, "oranges"]].
  3. Empty inventory:
    • If inventory is empty, the result is the shipment.
    • Example: [] and [[10, "apples"], [30, "bananas"], [20, "oranges"]] → [[10, "apples"], [30, "bananas"], [20, "oranges"]].
  4. Inventory with zeros and mixed shipment:
    • Update products with zero quantity and add new ones.
    • Example: [[0, "Bowling Ball"], [0, "Dirty Socks"], [0, "Hair Pin"], [0, "Microphone"]] and [[1, "Hair Pin"], [1, "Half-Eaten Apple"], [1, "Bowling Ball"], [1, "Toothpaste"]] → [[1, "Bowling Ball"], [0, "Dirty Socks"], [1, "Hair Pin"], [0, "Microphone"], [1, "Half-Eaten Apple"], [1, "Toothpaste"]].

Solution Development

Visual Approach (Mermaid)

flowchart TD
  A["Initial inventory"] --> B["Add products to Map"]
  C["New shipment"] --> D["Update Map (sum or add)"]
  B --> D
  D --> E["Build final inventory"]

Strategy

  1. Use a Map to store products and quantities.
  2. Iterate over the original inventory and register products in the Map.
  3. Iterate over the shipment:
    • If the product exists, sum the quantity.
    • If not, add it and record its order.
  4. Build the final array:
    • First, original products (with updated quantities).
    • Then, new products in the received order.

This method is efficient and clear, ideal for interviews and production.

Step-by-Step Implementation

function updateInventory(inventory, shipment) {
  const map = new Map()
  const originalOrder = []
  const newOnes = []

  // Register original inventory
  for (const [qty, prod] of inventory) {
    map.set(prod, qty)
    originalOrder.push(prod)
  }

  // Process shipment
  for (const [qty, prod] of shipment) {
    if (map.has(prod)) {
      map.set(prod, map.get(prod) + qty)
    }
    else {
      map.set(prod, qty)
      newOnes.push(prod)
    }
  }

  // Build result
  const result = []
  for (const prod of originalOrder) {
    result.push([map.get(prod), prod])
  }
  for (const prod of newOnes) {
    result.push([map.get(prod), prod])
  }
  return result
}

Complexity Analysis

Time Complexity

The algorithm iterates both arrays once and uses O(1)O(1) operations in the Map.

O(n+m)O(n + m)

where nn is the number of products in the inventory and mm in the shipment.

Space Complexity

Auxiliary structures are proportional to the total number of products:

O(n+m)O(n + m)

Edge Cases and Considerations

  • Empty inventory or shipment.
  • Products with zero quantity.
  • Repeated products in the shipment (the algorithm sums them).
  • Case sensitivity in product names.
  • Order: original order is preserved, new ones go at the end.

Reflections and Learnings

What did I learn?

  • Using Map simplifies updating and searching for products.
  • The algorithm is efficient and easy to understand.

Can it be optimized?

Only if memory is critical, but we would lose clarity and speed. For most cases, this approach is ideal.

Resources and References

freecodecamp daily-challenge