How do you solve Replace Employee ID With The Unique Identifier on LeetCode?

Replace Employee ID With The Unique Identifier (LeetCode #1378) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Using a HashMap allows for O(1) lookups, significantly speeding up the process.

What is the brute force solution for Replace Employee ID With The Unique Identifier?

The brute force approach for Replace Employee ID With The Unique Identifier is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves checking each employee in the Employees table against every entry in the EmployeeUNI table to find a match. This is straightforward but inefficient, especially with larger datasets. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Replace Employee ID With The Unique Identifier?

Replace Employee ID With The Unique Identifier uses the following concepts: Database. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Replace Employee ID With The Unique Identifier?

Always consider the data structure that can optimize your lookups. Think about edge cases, such as employees without unique IDs. Practice writing SQL queries to become comfortable with JOIN operations.

What are common mistakes when solving Replace Employee ID With The Unique Identifier?

Not handling cases where there are no matches properly, leading to incorrect outputs. Overlooking the use of JOINs which can simplify the solution.

#1378

Replace Employee ID With The Unique Identifier

Easy

DatabaseHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal solution uses a HashMap to store the unique IDs for quick lookups. This significantly reduces the time complexity by allowing us to find unique IDs in constant time.

⚙️

Algorithm

5 steps

1Step 1: Create a HashMap to store the unique_id for each id from the EmployeeUNI table.
2Step 2: Populate the HashMap with entries from EmployeeUNI.
3Step 3: Select the name from Employees and look up the unique_id in the HashMap.
4Step 4: If the id is not found in the HashMap, return null for unique_id.
5Step 5: Return the results.

solution.py4 lines

1# Full working Python code
2SELECT COALESCE(eu.unique_id, null) AS unique_id, e.name
3FROM Employees e
4LEFT JOIN EmployeeUNI eu ON e.id = eu.id;

ℹ

Complexity note: The time complexity is O(n) because we are iterating through the EmployeeUNI table once to create the HashMap, and then we perform a single pass through the Employees table.

1Using a HashMap allows for O(1) lookups, significantly speeding up the process.
2LEFT JOIN in SQL is a powerful tool for combining data from two tables based on a common key.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.