cw1_reverse_string_BEGIN
```python
def reverse_string(s: str) -> str:
    return s[::-1]
```
cw1_reverse_string_END

cw2_binary_search_BEGIN
```python
def binary_search(arr: list, target) -> int:
    lo, hi = 0, len(arr) - 1
    while lo <= hi:
        mid = (lo + hi) // 2
        if arr[mid] == target:
            return mid
        if arr[mid] < target:
            lo = mid + 1
        else:
            hi = mid - 1
    return -1
```
cw2_binary_search_END

cw3_parse_json_file_BEGIN
```python
import json
from pathlib import Path
from typing import Any, Union


def parse_json_file(path: Union[str, Path]) -> Any:
    with open(path, "r", encoding="utf-8") as f:
        return json.load(f)
```
cw3_parse_json_file_END

cw4_factorial_BEGIN
```python
def factorial(n: int) -> int:
    if not isinstance(n, int) or n < 0:
        raise ValueError("n must be a non-negative integer")
    result = 1
    for i in range(2, n + 1):
        result *= i
    return result
```
cw4_factorial_END

cw5_sort_dict_by_value_BEGIN
```python
def sort_dict_by_value(d: dict) -> dict:
    return dict(sorted(d.items(), key=lambda item: item[1], reverse=True))
```
cw5_sort_dict_by_value_END

cw6_debounce_decorator_BEGIN
```python
import threading
from functools import wraps


def debounce(wait_seconds: float):
    def decorator(func):
        lock = threading.Lock()
        timer = {"t": None}

        @wraps(func)
        def wrapper(*args, **kwargs):
            with lock:
                if timer["t"] is not None:
                    timer["t"].cancel()
                timer["t"] = threading.Timer(
                    wait_seconds, lambda: func(*args, **kwargs)
                )
                timer["t"].daemon = True
                timer["t"].start()

        return wrapper

    return decorator
```
cw6_debounce_decorator_END

cw7_count_word_frequencies_BEGIN
```python
import re
from collections import Counter


def count_word_frequencies(text: str) -> dict:
    words = re.findall(r"\b\w+\b", text.lower())
    return dict(Counter(words))
```
cw7_count_word_frequencies_END

cw8_validate_email_BEGIN
```python
import re

_EMAIL_RE = re.compile(r"^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$")


def is_valid_email(s: str) -> bool:
    if not isinstance(s, str):
        return False
    return _EMAIL_RE.match(s) is not None
```
cw8_validate_email_END
