Posts (238+)

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July 2026

Linux du and df:Find Disk Space Hogs

Hands-on df and du recipes — check filesystem free space, hunt directory hogs, and resolve “no space left on device” with confidence.

Data Structures

Pick the Right Structure:Match the Job to the Data Layout

A decision guide for the data-structures series: given the hot operation, which layout and which JDK type — with links to every post in the series.

Algorithms

Kadane:Maximum Subarray Without Trying Every Slice

Running best ending here, empty-array and all-negative pitfalls, and why this is one pass of DP you do not need to name as a table.

Data Structures

Quadtrees and k-d Trees:Space as a Tree Instead of a Nested Loop

Spatial trees split the plane so range and nearest-neighbor queries skip whole regions. Quadtrees cut into four boxes; k-d trees alternate axis splits.

Algorithms

Prefix Sums:Answer a Range in O(1) After One Precompute

Inclusive vs exclusive prefixes, a 2D sketch, difference arrays for range updates, and when a Fenwick or segment tree is the next bill.

Algorithms

Sliding Window:Grow and Shrink a Range Without Restarting the Scan

Fixed and variable windows, the add-right / drop-left invariant, and why this is not the same thing as a rate-limit window.

Data Structures

Suffix Arrays:Substring Search Without a Full Suffix Tree

A suffix array is the sorted list of a string’s suffixes as start indices. Binary search finds substrings; a short section contrasts the heavier suffix tree.

Data Structures

Treaps:BST Order Plus Heap Priority

A treap is a BST on keys and a heap on random priorities. Rotations restore heap order so the shape stays balanced in expectation without color bits.

Linux

Linux ss and netstat:Monitor Network Connections

Hands-on ss and netstat recipes — list listening sockets, inspect open connections, check routing tables, and read interface statistics.

Algorithms

Two Pointers:One Pass From Both Ends Instead of a Nested Loop

Opposite-end, pair-sum on sorted data, and fast/slow — when two indexes replace O(n²) and when they are just two indexes.