Programming notes, organised the way you study

Relative Sort Array

Relative Sort Array (LeetCode 1122): sort by the order defined in a second array, with the rest sorted ascending. O(n log n), Python/Java/C++.

Wiggle Sort

Wiggle Sort (LeetCode 280): rearrange so nums[0] = nums[2]

Wiggle Sort II

Wiggle Sort II (LeetCode 324): strict nums[0] < nums[1] > nums[2]... via sorting and interleaving the two halves in reverse. O(n log n), Python/Java/C...

H-Index (Sorting Approach)

H-Index (LeetCode 274) via sorting: sort citations descending and find the largest i where citations[i] >= i+1. O(n log n), Python/Java/C++.

Meeting Rooms (Can Attend All Meetings)

Meeting Rooms (LeetCode 252): sort meetings by start and check that none overlaps the previous one. O(n log n), Python/Java/C++.

Kth Largest Element (Sorting Approach)

Kth Largest Element (LeetCode 215) via sorting: sort and index from the end in O(n log n), with a note on the O(n)-average quickselect alternative.

Packages and __init__.py

A package is a directory of modules. __init__.py marks it and defines its public face, and relative imports let modules inside it find each other.

Find the Second Largest Element in an Array

Scope and the LEGB Rule

Python resolves a name by looking in four places in a fixed order: local, enclosing, global, built-in. Assignment anywhere in a function makes the nam...

Paths and Directories with pathlib

pathlib turns file paths into objects with methods. It replaces string joining and most of os.path, and it works the same on Windows, macOS and Linux.

PRIMARY KEY and FOREIGN KEY

The two constraints that give a database its structure: one that identifies a row, and one that guarantees a reference points at something real.

Ordered and Unordered Lists

ul when the order does not matter, ol when it does. Plus the start, reversed, type and value attributes that most people never discover.