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Display Table of Food Orders in a Restaurant

Difficulty: Medium

Problem Description

Given the array orders, which represents the orders that customers have done in a restaurant. More specifically orders[i]=[customerNamei,tableNumberi,foodItemi] where customerNamei is the name of the customer, tableNumberi is the table customer sit at, and foodItemi is the item customer orders.

Return the restaurant's "display table". The "display table" is a table whose row entries denote how many of each food item each table ordered. The first column is the table number and the remaining columns correspond to each food item in alphabetical order. The first row should be a header whose first column is "Table", followed by the names of the food items. Note that the customer names are not part of the table. Additionally, the rows should be sorted in numerically increasing order.

Key Insights

  • The input consists of a list of orders with details about customer name, table number, and food item.
  • We need to aggregate the orders by table number and food item.
  • The output must be sorted with tables in increasing order and food items in alphabetical order.
  • Using a hash table (dictionary) can efficiently store the count of food items per table.

Space and Time Complexity

Time Complexity: O(n + m log m), where n is the number of orders and m is the number of unique food items. The sorting of food items contributes to the log factor.

Space Complexity: O(m + t), where m is the number of unique food items and t is the number of tables.

Solution

To solve the problem, we will use a hash table (or dictionary) to store the count of food items for each table. The steps are as follows:

  1. Parse the input list of orders to populate a dictionary where keys are table numbers and values are another dictionary that holds food items and their counts.
  2. Extract the unique food items and sort them alphabetically.
  3. Prepare the final output table with the header row containing "Table" followed by the sorted food items.
  4. For each table, create a row where the first column is the table number and the remaining columns are counts of each food item (0 if the item was not ordered).
  5. Return the completed display table.

Code Solutions

def displayTable(orders):
    from collections import defaultdict
    
    table_orders = defaultdict(lambda: defaultdict(int))
    food_items = set()
    
    for customerName, tableNumber, foodItem in orders:
        table_orders[tableNumber][foodItem] += 1
        food_items.add(foodItem)
    
    sorted_tables = sorted(table_orders.keys(), key=int)
    sorted_food_items = sorted(food_items)
    
    result = [["Table"] + sorted_food_items]
    
    for table in sorted_tables:
        row = [table]
        for food in sorted_food_items:
            row.append(table_orders[table][food])
        result.append(row)
    
    return result
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