--description--

Given a 2D array representing the inventory of your store, and another 2D array representing a shipment you have received, return your updated inventory.

• Each element in the arrays will have the format: [quantity, "item"], where quantity is an integer and "item" is a string.
• Update items in the inventory by adding the quantity of any matching items from the shipment.
• If a received item does not exist in the current inventory, add it as a new entry to the end of the inventory.
• Return inventory in the order it was given with new items at the end in the order they appear in the shipment.

For example, given an inventory of [[2, "apples"], [5, "bananas"]] and a shipment of [[1, "apples"], [3, "bananas"]], return [[3, "apples"], [8, "bananas"]].

--hints--

updateInventory([[2, "apples"], [5, "bananas"]], [[1, "apples"], [3, "bananas"]]) should return [[3, "apples"], [8, "bananas"]].

assert.deepEqual(updateInventory([[2, "apples"], [5, "bananas"]], [[1, "apples"], [3, "bananas"]]), [[3, "apples"], [8, "bananas"]]);

updateInventory([[2, "apples"], [5, "bananas"]], [[1, "apples"], [3, "bananas"], [4, "oranges"]]) should return [[3, "apples"], [8, "bananas"], [4, "oranges"]].

assert.deepEqual(updateInventory([[2, "apples"], [5, "bananas"]], [[1, "apples"], [3, "bananas"], [4, "oranges"]]), [[3, "apples"], [8, "bananas"], [4, "oranges"]]);

updateInventory([], [[10, "apples"], [30, "bananas"], [20, "oranges"]]) should return [[10, "apples"], [30, "bananas"], [20, "oranges"]].

assert.deepEqual(updateInventory([], [[10, "apples"], [30, "bananas"], [20, "oranges"]]), [[10, "apples"], [30, "bananas"], [20, "oranges"]]);

updateInventory([[0, "Bowling Ball"], [0, "Dirty Socks"], [0, "Hair Pin"], [0, "Microphone"]], [[1, "Hair Pin"], [1, "Half-Eaten Apple"], [1, "Bowling Ball"], [1, "Toothpaste"]]) should return [[1, "Bowling Ball"], [0, "Dirty Socks"], [1, "Hair Pin"], [0, "Microphone"], [1, "Half-Eaten Apple"], [1, "Toothpaste"]].

assert.deepEqual(updateInventory([[0, "Bowling Ball"], [0, "Dirty Socks"], [0, "Hair Pin"], [0, "Microphone"]], [[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"]]);

--seed--

--seed-contents--

function updateInventory(inventory, shipment) {
  return inventory;
}

--solutions--

function updateInventory(inventory, shipment) {
  const inventoryMap = new Map();
  inventory.forEach(([qty, item], index) => {
    inventoryMap.set(item, index);
  });

  shipment.forEach(([qty, item]) => {
    if (inventoryMap.has(item)) {
      const index = inventoryMap.get(item);
      inventory[index][0] += qty;
    } else {
      inventory.push([qty, item]);
      inventoryMap.set(item, inventory.length - 1);
    }
  });

  return inventory;
}