Find the middle node using slow/fast pointers.
Split the list into two halves.
Recursively sort each half.
Merge the sorted halves.
Unlike arrays, splitting a linked list is but doesn't require extra space. The merge step is also in-place.
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$ curl repovive.com/roadmaps/fundamental-algorithms/divide-and-conquer/sort-list-merge-sort-on-lists
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