Posts (238+)

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July 2026

Heapsort:Sort With a Heap When You Need O(n log n) and Little Extra Memory

Build a max-heap and extract the max into the tail — guaranteed O(n log n), little extra memory, and why PriorityQueue poll-all is not this procedure.

Java

Collections and Arrays:Sort, Wrap, Copy, and the Methods You Forget

Use Collections and Arrays for sort, binarySearch, shuffle, nCopies, emptyXxx, synchronized wrappers, and asList — the static methods around the types, not a fourth List implementation.

Algorithms

Quicksort:Partition in Place and Why the Pivot Policy Is the Algorithm

Partition around a pivot and recurse — and why last-element vs random vs median-of-three vs dual-pivot is the algorithm, not textbook Lomuto as Arrays.sort.

Java

Collection Factories:`List.of` and `Map.copyOf` Without the Mutable Default

Use List.of, Set.of, Map.of, and copyOf for unmodifiable collections that reject nulls — Java 9 factories, not Collections.unmodifiableList wrapping a live ArrayList.

Linux

Linux sudo and /etc/sudoers:Manage Privileged Access with Intent

Hands-on sudo and sudoers recipes — run commands as root or another user, edit policy safely with visudo, and delegate fine-grained privileges without handing out full root.

Algorithms

Merge Sort:Stable Divide-and-Conquer When You Can Afford the Extra Array

Split, sort the halves, merge two sorted runs — why the extra array buys a guaranteed O(n log n) bound and stability, and what object Arrays.sort actually runs.

Algorithms

Quadratic Sorts:Insertion, Selection, and Why Bubble Survives Only in Interviews

Insertion still earns a seat on small or nearly-sorted ranges; selection swaps the min into place; bubble is a whiteboard name — none of them are the production default.

Java

IdentityHashMap and WeakHashMap:== Keys and GC-able Keys

Use IdentityHashMap when keys are compared with ==, and WeakHashMap when the GC should drop entries whose keys are otherwise unreachable — two unusual maps, two different jobs.

Java

EnumSet and EnumMap:Universe-Sized Keys Without a Hash

Use EnumSet and EnumMap when the key universe is an enum — a bit vector and an ordinal array, not a hash table.

Algorithms

Merge Intervals:Collapse Overlaps Instead of Sorting the Same Range Twice

Sort by start, sweep, and merge overlapping calendar or busy ranges — and when this is not interval scheduling.