Is Find Cities in Each State easy or hard?

Find Cities in Each State is considered an Easy database problem. It mainly tests familiarity with GROUP BY aggregation and basic SQL data summarization rather than complex algorithms.

Find Cities in Each State Python/Java solution

In SQL (commonly used with Java backends), use GROUP BY with GROUP_CONCAT to aggregate city names. In Python data workflows, use Pandas groupby('state') and aggregate the city column by joining values into a single string per group.

How to solve Find Cities in Each State in O(n)?

Use a GROUP BY query on the state column and aggregate the city column using a function such as GROUP_CONCAT. The database engine builds groups while scanning rows once, making the overall complexity O(n). Pandas achieves the same complexity using groupby() and aggregation.

What is the best approach for Find Cities in Each State?

The most efficient approach uses SQL aggregation with GROUP BY. Group rows by the state column and aggregate city names using functions like GROUP_CONCAT in MySQL. This processes the table in O(n) time and produces one row per state with all cities combined.

Is Find Cities in Each State asked at Google/Amazon/Meta?

Database aggregation questions like this appear frequently in SQL interview rounds at companies such as Amazon, Meta, and Google. Candidates are expected to understand GROUP BY, aggregation functions, and how relational databases summarize grouped data.

What data structure is used in Find Cities in Each State?

Conceptually the solution relies on grouping by a key, which behaves like a hash map from state to a list of cities. SQL databases implement this internally using hashing or sorting during GROUP BY execution.

What is the time complexity of Find Cities in Each State?

The grouping and aggregation solution runs in O(n) time where n is the number of rows in the table. The database scans the table once and groups rows by state. Space complexity is O(n) for storing grouped results.

3198. Find Cities in Each State - Practice Online

Table: cities

+-------------+---------+
| Column Name | Type    | 
+-------------+---------+
| state       | varchar |
| city        | varchar |
+-------------+---------+
(state, city) is the primary key (combination of columns with unique values) for this table.
Each row of this table contains the state name and the city name within that state.

Write a solution to find all the cities in each state and combine them into a single comma-separated string.

Return the result table ordered by state and city in ascending order.

The result format is in the following example.

Example:

Input:

cities table:

+-------------+---------------+
| state       | city          |
+-------------+---------------+
| California  | Los Angeles   |
| California  | San Francisco |
| California  | San Diego     |
| Texas       | Houston       |
| Texas       | Austin        |
| Texas       | Dallas        |
| New York    | New York City |
| New York    | Buffalo       |
| New York    | Rochester     |
+-------------+---------------+

Output:

+-------------+---------------------------------------+
| state       | cities                                |
+-------------+---------------------------------------+
| California  | Los Angeles, San Diego, San Francisco |
| New York    | Buffalo, New York City, Rochester     |
| Texas       | Austin, Dallas, Houston               |
+-------------+---------------------------------------+

Explanation:

California: All cities ("Los Angeles", "San Diego", "San Francisco") are listed in a comma-separated string.
New York: All cities ("Buffalo", "New York City", "Rochester") are listed in a comma-separated string.
Texas: All cities ("Austin", "Dallas", "Houston") are listed in a comma-separated string.

Note: The output table is ordered by the state name in ascending order.