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Exchange Seats.md

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Algorithm

There are 3 cases

  1. For students with even-numbered ids, subtract 1 from their id
  2. For students with odd-numbered ids, add 1 to their id (Except if this odd-numbered student has the highest id in the class
  3. For student with odd-numbered id who also has the highest id in the class, don't change the id.

MySQL Solution

SELECT
    CASE
        WHEN id % 2 = 0 THEN id - 1
        WHEN id % 2 = 1 AND id != (SELECT COUNT(*) FROM seat) THEN id + 1
        ELSE id
    END as id,
    student
FROM seat
ORDER BY id

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