Exchange Seats - Practice Coding Problems

Exchange Seats - Problem

Database Medium

Given a Seat table with columns id and student, write a SQL solution to swap the seat id of every two consecutive students.

Rules:

If the number of students is odd, the id of the last student is not swapped
Return the result table ordered by id in ascending order

The table structure is:

Seat table:

id (int): Primary key, starts from 1 and increments continuously
student (varchar): Name of the student

Table Schema

Seat

Column Name	Type	Description
`id` PK	int	Primary key, seat identifier starting from 1
`student`	varchar	Name of the student

Primary Key: id

Note: The ID sequence always starts from 1 and increments continuously

Input & Output

Example 1 — Basic Seat Swapping

Input Table:

id	student
1	Alice
2	Bob
3	Charlie
4	David
5	Eve

Output:

id	student
1	Bob
2	Alice
3	David
4	Charlie
5	Eve

💡 Note:

Students are swapped in pairs: (1,2) swap to become (Bob,Alice), (3,4) swap to become (David,Charlie). Student 5 (Eve) has no pair, so remains in the same position.

Example 2 — Even Number of Students

Input Table:

id	student
1	Alice
2	Bob

Output:

id	student
1	Bob
2	Alice

💡 Note:

With an even number of students, all students have pairs. Alice and Bob swap positions completely.

Example 3 — Single Student

Input Table:

id	student
1	Alice

Output:

id	student
1	Alice

💡 Note:

With only one student, there's no one to swap with, so Alice remains in seat 1.

Constraints

1 ≤ id ≤ 50
student is a non-empty string
id is a continuous sequence starting from 1

Visualization

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Understanding the Visualization

Input

Original seat assignments

CASE WHEN

Apply swap logic

Output

Students in swapped seats

Key Takeaway

🎯 Key Insight: Use modulo operation to identify odd/even seats and conditionally swap with CASE WHEN logic

Asked in

f Facebook 12 M Microsoft 8

Use CASE WHEN with modulo operation to conditionally swap seat assignments: increment odd IDs (if not last), decrement even IDs, keeping the final odd student in place.

Table Schema

Seat

Column Name	Type	Description
`id` PK	int	Primary key, seat identifier starting from 1
`student`	varchar	Name of the student

Primary Key: id

Note: The ID sequence always starts from 1 and increments continuously

Common Approaches

Approach	Time	Space	Notes
✓ Conditional Swapping with CASE WHEN	O(n)	O(1)	Use CASE WHEN to conditionally increment/decrement IDs for swapping

Conditional Swapping with CASE WHEN — Algorithm Steps

Step 1: Use CASE WHEN to check if id is odd or even
Step 2: For odd IDs, try to swap with id+1 if it exists
Step 3: For even IDs, swap with id-1
Step 4: Order final result by id

Visualization

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Step-by-Step Walkthrough

Check ID

Determine if ID is odd or even

Apply Logic

Increment odd, decrement even

Handle Edge

Last odd student stays

Code -

solution.c — C

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single scan through table

✓ Linear Growth

Space Complexity

O(1)

No additional space needed

✓ Linear Space

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Smart Actions

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Table Schema

Input & Output

Constraints

Visualization

Related Problems

Table Schema

Common Approaches

Conditional Swapping with CASE WHEN — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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