LeetCode 1418: Display Table of Food Orders in a Restaurant Solution

Master LeetCode problem 1418 (Display Table of Food Orders in a Restaurant), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1418. Display Table of Food Orders in a Restaurant

Medium

Array Hash Table String Sorting Ordered Set

Problem Explanation

Explanation

To solve this problem, we need to iterate over the orders and create a mapping of table numbers to the count of each food item ordered by that table. We can achieve this by using a hashmap where the key is the table number and the value is another hashmap that maps food items to their count.

Create a hashmap tableOrders to store the mapping of table numbers to the count of each food item ordered.
Iterate through the orders and update the tableOrders hashmap accordingly.
Extract the unique food items from all orders and sort them in alphabetical order.
Create the result table, with the first row containing the food items in alphabetical order.
Iterate through the table numbers in sorted order and populate the counts of food items for each table accordingly.

Time complexity: O(n * m) where n is the number of orders and m is the average number of unique food items per order. Space complexity: O(n * m) for the hashmap storing the table orders. Java:

Solution Code

class Solution {
    public List<List<String>> displayTable(List<List<String>> orders) {
        Map<Integer, Map<String, Integer>> tableOrders = new TreeMap<>();
        
        Set<String> foodItems = new TreeSet<>();
        
        for (List<String> order : orders) {
            int tableNum = Integer.parseInt(order.get(1));
            String foodItem = order.get(2);
            
            foodItems.add(foodItem);
            
            tableOrders.putIfAbsent(tableNum, new TreeMap<>());
            Map<String, Integer> foodCount = tableOrders.get(tableNum);
            foodCount.put(foodItem, foodCount.getOrDefault(foodItem, 0) + 1);
        }
        
        List<List<String>> result = new ArrayList<>();
        
        List<String> header = new ArrayList<>();
        header.add("Table");
        header.addAll(foodItems);
        result.add(header);
        
        for (Map.Entry<Integer, Map<String, Integer>> entry : tableOrders.entrySet()) {
            List<String> row = new ArrayList<>();
            row.add(String.valueOf(entry.getKey()));
            for (String foodItem : foodItems) {
                row.add(String.valueOf(entry.getValue().getOrDefault(foodItem, 0)));
            }
            result.add(row);
        }
        
        return result;
    }
}

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