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

cw2_binary_search_BEGIN
```python
def binary_search(arr, target):
    low, high = 0, len(arr) - 1
    while low <= high:
        mid = (low + high) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            low = mid + 1
        else:
            high = mid - 1
    return -1
```
cw2_binary_search_END

cw3_parse_json_file_BEGIN
```python
import json

def parse_json_file(path):
    with open(path, 'r') as f:
        return json.load(f)
```
cw3_parse_json_file_END

cw4_factorial_BEGIN
```python
def factorial(n):
    if n < 0:
        raise ValueError("n must be non-negative")
    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):
    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):
    def decorator(func):
        timer = None
        lock = threading.Lock()

        @wraps(func)
        def wrapper(*args, **kwargs):
            nonlocal timer
            with lock:
                if timer is not None:
                    timer.cancel()
                timer = threading.Timer(wait_seconds, func, args=args, kwargs=kwargs)
                timer.start()
        return wrapper
    return decorator
```
cw6_debounce_decorator_END

cw7_count_word_frequencies_BEGIN
```python
def count_word_frequencies(text):
    freq = {}
    for word in text.split():
        freq[word] = freq.get(word, 0) + 1
    return freq
```
cw7_count_word_frequencies_END

cw8_validate_email_BEGIN
```python
import re

EMAIL_REGEX = re.compile(r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$')

def is_valid_email(s):
    return bool(EMAIL_REGEX.match(s))
```
cw8_validate_email_END
