Solved -> 626. Exchange Seats

Author: NandiSoham

06_Subqueries/626. Exchange Seats.sql

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+/* 
+
+Problem Link -> https://leetcode.com/problems/exchange-seats/description/?envType=study-plan-v2&envId=top-sql-50
+
+------------------------------------------------------------- QUESTION -----------------------------------------------------------
+
+Table: Seat
+
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| id          | int     |
+| student     | varchar |
++-------------+---------+
+id is the primary key (unique value) column for this table.
+Each row of this table indicates the name and the ID of a student.
+id is a continuous increment.
+ 
+
+Write a solution to swap the seat id of every two consecutive students. 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 result format is in the following example.
+ 
+
+Example 1:
+
+Input: 
+Seat table:
++----+---------+
+| id | student |
++----+---------+
+| 1  | Abbot   |
+| 2  | Doris   |
+| 3  | Emerson |
+| 4  | Green   |
+| 5  | Jeames  |
++----+---------+
+
+Output: 
++----+---------+
+| id | student |
++----+---------+
+| 1  | Doris   |
+| 2  | Abbot   |
+| 3  | Green   |
+| 4  | Emerson |
+| 5  | Jeames  |
++----+---------+
+
+Explanation: 
+Note that if the number of students is odd, there is no need to change the last one's seat.
+
+*/
+
+-- ----------------------------------------------------------- SOLUTION -----------------------------------------------------------
+
+SELECT
+    CASE
+        WHEN
+            id = (SELECT MAX(id) FROM SEAT) AND MOD(id,2) = 1
+            THEN id 
+        WHEN MOD(id,2) = 1 THEN id + 1
+        ELSE id - 1
+    END AS id, student
+FROM Seat
+ORDER BY id
+