Given a matrix x with n rows and m columns, return a matrix y with 2n rows and m columns, such that every column in x is sorted from low to high and then from high to low.

Example:

x = 8  9  3  9
    9  6  5  2
    2  1  9  9

y = 2  1  3  2
    8  6  5  9
    9  9  9  9
    9  9  9  9
    8  6  5  9
    2  1  3  2
Solve

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Last Solution submitted on Jan 04, 2026

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Vasilis Bellos Chiara qiushui wu

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