### Build a Simple HTTP Server with Python

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Demonstrates a basic HTTP server using Python's socket library. It listens on a specified port, accepts incoming connections, and returns a static 'Hello, World!' response.

```python
import socket

def handle_request(request):
    http_response = b"HTTP/1.1 200 OK\n\nHello, World!\n"
    return http_response

def serve_forever():
    listen_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    listen_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    listen_socket.bind(('', 8888))
    listen_socket.listen(1)
    while True:
        client_connection, client_address = listen_socket.accept()
        request = client_connection.recv(1024)
        http_response = handle_request(request)
        client_connection.sendall(http_response)
        client_connection.close()
```

--------------------------------

### Operating System: Kernel Entry Point (C)

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Provides a basic C implementation for a kernel's entry point, demonstrating how to interact with video memory to display text on the screen. This snippet is foundational for understanding OS development.

```c
// Example: Simple kernel entry point (from Kernel 101)
void kernel_main(void) {
    const char *str = "Hello, Kernel World!";
    char *vidptr = (char*)0xb8000;  // Video memory address
    unsigned int i = 0;
    unsigned int j = 0;

    // Clear screen
    while (j < 80 * 25 * 2) {
        vidptr[j] = ' ';
        vidptr[j+1] = 0x07;
        j = j + 2;
    }

    // Print string
    j = 0;
    while (str[j] != '\0') {
        vidptr[i] = str[j];
        vidptr[i+1] = 0x07;
        ++j;
        i = i + 2;
    }
}
```

--------------------------------

### Create a Minimal Container with Go

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Uses Linux namespaces and syscalls to create an isolated process environment. It demonstrates process isolation by setting hostnames and chrooting the filesystem.

```go
package main
import ("fmt", "os", "os/exec", "syscall")

func main() {
    switch os.Args[1] {
    case "run": run()
    case "child": child()
    }
}

func run() {
    cmd := exec.Command("/proc/self/exe", append([]string{"child"}, os.Args[2:]...)...)
    cmd.SysProcAttr = &syscall.SysProcAttr{Cloneflags: syscall.CLONE_NEWUTS | syscall.CLONE_NEWPID | syscall.CLONE_NEWNS}
    cmd.Run()
}

func child() {
    syscall.Sethostname([]byte("container"))
    syscall.Chroot("/")
    cmd := exec.Command(os.Args[2], os.Args[3:]...)
    cmd.Run()
}
```

--------------------------------

### Implement Unix Shell Command Parsing and Process Management in C

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

This snippet demonstrates the core loop of a Unix shell, including tokenizing input strings and spawning child processes using fork and execvp. It handles basic command execution and process synchronization using waitpid.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>

#define LSH_TOK_BUFSIZE 64
#define LSH_TOK_DELIM " \t\r\n\a"

char **lsh_split_line(char *line) {
    int bufsize = LSH_TOK_BUFSIZE, position = 0;
    char **tokens = malloc(bufsize * sizeof(char*));
    char *token;

    token = strtok(line, LSH_TOK_DELIM);
    while (token != NULL) {
        tokens[position] = token;
        position++;
        token = strtok(NULL, LSH_TOK_DELIM);
    }
    tokens[position] = NULL;
    return tokens;
}

int lsh_launch(char **args) {
    pid_t pid, wpid;
    int status;

    pid = fork();
    if (pid == 0) {
        if (execvp(args[0], args) == -1) {
            perror("lsh");
        }
        exit(EXIT_FAILURE);
    } else if (pid < 0) {
        perror("lsh");
    } else {
        do {
            wpid = waitpid(pid, &status, WUNTRACED);
        } while (!WIFEXITED(status) && !WIFSIGNALED(status));
    }
    return 1;
}
```

--------------------------------

### Train a Neural Network with Python

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Implements a basic feedforward neural network using NumPy. It demonstrates weight initialization, forward propagation, and backpropagation to train the model over 60,000 iterations.

```python
syn0 = 2 * np.random.random((3,4)) - 1
syn1 = 2 * np.random.random((4,1)) - 1

for j in range(60000):
    l0 = X
    l1 = sigmoid(np.dot(l0, syn0))
    l2 = sigmoid(np.dot(l1, syn1))
    l2_error = y - l2
    l2_delta = l2_error * sigmoid(l2, deriv=True)
    l1_error = l2_delta.dot(syn1.T)
    l1_delta = l1_error * sigmoid(l1, deriv=True)
    syn1 += l1.T.dot(l2_delta)
    syn0 += l0.T.dot(l1_delta)
```

--------------------------------

### Neural Network: Simple Network Implementation (Python)

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Demonstrates the implementation of a basic neural network in Python using NumPy. It includes the sigmoid activation function and its derivative, along with the initialization of input and output datasets.

```python
# Example: Simple neural network (from A Neural Network in 11 lines of Python)
import numpy as np

# Sigmoid function and derivative
def sigmoid(x, deriv=False):
    if deriv:
        return x * (1 - x)
    return 1 / (1 + np.exp(-x))

# Input dataset
X = np.array([[0,0,1], [0,1,1], [1,0,1], [1,1,1]])
# Output dataset
y = np.array([[0], [1], [1], [0]])

# Seed random numbers
np.random.seed(1)

```

--------------------------------

### Implement a Blockchain with Python

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Provides a foundational blockchain structure including block creation, hashing using SHA-256, and a proof-of-work algorithm to validate blocks.

```python
import hashlib, json
from time import time

class Blockchain:
    def __init__(self):
        self.chain = []
        self.current_transactions = []
        self.new_block(previous_hash='1', proof=100)

    def new_block(self, proof, previous_hash=None):
        block = {'index': len(self.chain) + 1, 'timestamp': time(), 'transactions': self.current_transactions, 'proof': proof, 'previous_hash': previous_hash or self.hash(self.chain[-1])}
        self.current_transactions = []
        self.chain.append(block)
        return block

    @staticmethod
    def hash(block):
        return hashlib.sha256(json.dumps(block, sort_keys=True).encode()).hexdigest()

    def proof_of_work(self, last_proof):
        proof = 0
        while self.valid_proof(last_proof, proof) is False: proof += 1
        return proof

    @staticmethod
    def valid_proof(last_proof, proof):
        return hashlib.sha256(f'{last_proof}{proof}'.encode()).hexdigest()[:4] == "0000"
```

--------------------------------

### Implement Virtual DOM and Rendering in JavaScript

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

This snippet demonstrates a minimal React-like library. It includes functions for creating virtual DOM elements and a recursive renderer that transforms these objects into actual browser DOM nodes.

```javascript
function createElement(type, props, ...children) {
    return {
        type,
        props: {
            ...props,
            children: children.map(child =>
                typeof child === "object" ? child : createTextElement(child)
            ),
        },
    };
}

function createTextElement(text) {
    return {
        type: "TEXT_ELEMENT",
        props: {
            nodeValue: text,
            children: [],
        },
    };
}

function render(element, container) {
    const dom = element.type === "TEXT_ELEMENT"
        ? document.createTextNode("")
        : document.createElement(element.type);

    Object.keys(element.props)
        .filter(key => key !== "children")
        .forEach(name => {
            dom[name] = element.props[name];
        });

    element.props.children.forEach(child => render(child, dom));
    container.appendChild(dom);
}

const element = createElement(
    "div",
    { id: "foo" },
    createElement("a", null, "bar"),
    createElement("b")
);
render(element, document.getElementById("root"));
```

--------------------------------

### 3D Renderer: Ray-Sphere Intersection and Render Loop (C++)

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Demonstrates fundamental concepts in 3D graphics rendering, including calculating ray-sphere intersections and the basic structure of a render loop. This snippet is useful for understanding the core logic behind ray tracing.

```cpp
// Example: Basic ray-sphere intersection (from Ray Tracing in One Weekend)
bool hit_sphere(const vec3& center, double radius, const ray& r) {
    vec3 oc = r.origin() - center;
    auto a = dot(r.direction(), r.direction());
    auto b = 2.0 * dot(oc, r.direction());
    auto c = dot(oc, oc) - radius*radius;
    auto discriminant = b*b - 4*a*c;
    return (discriminant > 0);
}

// Render loop
for (int j = image_height-1; j >= 0; --j) {
    for (int i = 0; i < image_width; ++i) {
        auto u = double(i) / (image_width-1);
        auto v = double(j) / (image_height-1);
        ray r(origin, lower_left_corner + u*horizontal + v*vertical - origin);
        color pixel_color = ray_color(r);
        write_color(std::cout, pixel_color);
    }
}
```

--------------------------------

### Implement Git Object Storage in Python

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

This module provides functions to write and read Git objects from the file system. It handles object serialization, SHA-1 hashing, and zlib compression to mimic Git's internal storage mechanism.

```python
import hashlib
import zlib
import os

def object_write(repo, obj):
    data = obj.serialize()
    result = obj.fmt + b' ' + str(len(data)).encode() + b'\x00' + data
    sha = hashlib.sha1(result).hexdigest()
    path = os.path.join(repo.gitdir, "objects", sha[0:2], sha[2:])
    os.makedirs(os.path.dirname(path), exist_ok=True)
    with open(path, 'wb') as f:
        f.write(zlib.compress(result))
    return sha

def object_read(repo, sha):
    path = os.path.join(repo.gitdir, "objects", sha[0:2], sha[2:])
    with open(path, "rb") as f:
        raw = zlib.decompress(f.read())
    x = raw.find(b' ')
    fmt = raw[0:x]
    y = raw.find(b'\x00', x)
    size = int(raw[x:y].decode("ascii"))
    return raw[y+1:]
```

--------------------------------

### Programming Language: Lisp Interpreter (Python)

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

A Python implementation of a simple Lisp interpreter, covering tokenization, parsing, and basic expression evaluation. This snippet is valuable for learning about language design and interpreter implementation.

```python
# Example: Simple Lisp interpreter (from How to Write a Lisp Interpreter in Python)
def tokenize(chars):
    """Convert a string of characters into a list of tokens."""
    return chars.replace('(', ' ( ').replace(')', ' ) ').split()

def parse(program):
    """Read a Scheme expression from a string."""
    return read_from_tokens(tokenize(program))

def read_from_tokens(tokens):
    """Read an expression from a sequence of tokens."""
    if len(tokens) == 0:
        raise SyntaxError('unexpected EOF')
    token = tokens.pop(0)
    if token == '(':
        L = []
        while tokens[0] != ')':
            L.append(read_from_tokens(tokens))
        tokens.pop(0)  # pop off ')'
        return L
    elif token == ')':
        raise SyntaxError('unexpected )')
    else:
        return atom(token)

def atom(token):
    """Numbers become numbers; every other token is a symbol."""
    try: return int(token)
    except ValueError:
        try: return float(token)
        except ValueError:
            return Symbol(token)
```

--------------------------------

### Implement Regex Engine Matching Logic in JavaScript

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

A lightweight regex matcher implementation using recursive backtracking. It supports basic character matching, the dot wildcard, start/end anchors, and the Kleene star operator.

```javascript
function match(pattern, text) {
    if (pattern[0] === '^') {
        return matchHere(pattern.slice(1), text);
    }
    let idx = 0;
    do {
        if (matchHere(pattern, text.slice(idx))) {
            return true;
        }
    } while (idx++ < text.length);
    return false;
}

function matchHere(pattern, text) {
    if (pattern.length === 0) return true;
    if (pattern[1] === '*') {
        return matchStar(pattern[0], pattern.slice(2), text);
    }
    if (pattern[0] === '$' && pattern.length === 1) {
        return text.length === 0;
    }
    if (text.length !== 0 && (pattern[0] === '.' || pattern[0] === text[0])) {
        return matchHere(pattern.slice(1), text.slice(1));
    }
    return false;
}

function matchStar(c, pattern, text) {
    do {
        if (matchHere(pattern, text)) return true;
    } while (text.length !== 0 && (text[0] === c || c === '.') && (text = text.slice(1)));
    return false;
}
```

--------------------------------

### Database: B-Tree Node Structure (C)

Source: https://context7.com/codecrafters-io/build-your-own-x/llms.txt

Illustrates the structure of internal and leaf nodes within a B-Tree, a common data structure for database indexing. This C code defines headers and helper functions for accessing key-value pairs in leaf nodes.

```c
// Example: Simple B-Tree node structure (from Let's Build a Simple Database)
typedef struct {
    uint32_t num_cells;
    uint32_t right_child;
} InternalNodeHeader;

typedef struct {
    uint32_t num_cells;
    uint32_t next_leaf;
} LeafNodeHeader;

void* leaf_node_cell(void* node, uint32_t cell_num) {
    return node + LEAF_NODE_HEADER_SIZE + cell_num * LEAF_NODE_CELL_SIZE;
}

void* leaf_node_key(void* node, uint32_t cell_num) {
    return leaf_node_cell(node, cell_num);
}

void* leaf_node_value(void* node, uint32_t cell_num) {
    return leaf_node_cell(node, cell_num) + LEAF_NODE_KEY_SIZE;
}
```

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