Intermediate code explainers

python

from collections import deque
 
 
def bfs(graph, start):

Breadth-first search and shortest paths in Python

graph-traversal bfs queue

Intermediate 9 steps

go

package middleware
 
import (
	"net/http"

Building a bearer-token auth middleware in Gin

middleware authentication closures

Intermediate 5 steps

javascript

function depthFirstSearch(graph, start) {
  const visited = new Set();
  const order = [];

Depth-first search and pathfinding in JS

graphs recursion depth-first-search

Intermediate 8 steps

typescript

// A module-scoped Singleton: the single instance lives in this module's
// closure and is never exposed directly.
 
interface AppConfig {

A module-scoped Singleton in TypeScript

singleton generics encapsulation

Intermediate 7 steps

ruby

class ThreadSafeCounter
  def initialize(initial = 0)
    @count = initial
    @mutex = Mutex.new

A thread-safe counter with Mutex in Ruby

concurrency mutex thread-safety

Intermediate 6 steps

php

<?php
 
namespace App\Models;

Accessors, mutators & casts in a Laravel model

eloquent accessors mutators

Intermediate 6 steps

java

import java.util.*;
 
public class TopologicalSort {

Topological sort with Kahn's algorithm

graphs topological-sort bfs

Intermediate 6 steps

java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

Java try-with-resources and AutoCloseable

try-with-resources autocloseable resource-management

Intermediate 6 steps

typescript

interface RetryOptions {
  retries?: number;
  baseDelayMs?: number;
  maxDelayMs?: number;

Retrying async tasks with exponential backoff

retry exponential-backoff async

Intermediate 8 steps

javascript

function debounce(fn, delay) {
  let timeoutId = null;
 
  function debounced(...args) {

Building a debounce function in JavaScript

closures timers higher-order-functions

Intermediate 6 steps

go

package main
 
import "fmt"

How Go slices grow and share memory

slices memory append

Intermediate 7 steps

java

import java.util.Arrays;
 
public class SlidingWindow {
    // Returns the maximum sum of any contiguous subarray of length k.

The sliding window technique in Java

sliding-window arrays algorithms

Intermediate 8 steps

python

def two_sum_sorted(numbers, target):
    """Find indices of two values that sum to target in a sorted array."""
    left, right = 0, len(numbers) - 1
    while left < right:

Two-pointer search on sorted arrays

two-pointers arrays sorting

Intermediate 9 steps

go

package main
 
import "sync"

Mutex vs RWMutex in Go

concurrency mutex synchronization

Intermediate 6 steps

ruby

# Binary search using Ruby's built-in Array#bsearch.
#
# There are two modes:
#   1. find-minimum mode  -> block returns true/false (monotonic)

Binary search patterns with Ruby's bsearch

binary-search algorithms ranges

Intermediate 7 steps

typescript

type NestedArray<T> = Array<T | NestedArray<T>>;
 
function flatten<T>(input: NestedArray<T>): T[] {
  const result: T[] = [];

Recursively flattening nested arrays in TypeScript

recursion recursive-types generics

Intermediate 7 steps

java

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;

Breadth-first search on an adjacency-list graph

graph-traversal bfs adjacency-list

Intermediate 7 steps

javascript

function flatten(arr) {
  const result = [];
  for (const item of arr) {
    if (Array.isArray(item)) {

Flattening nested arrays with recursion

recursion arrays reduce

Intermediate 7 steps