"""
This program finds common words between two strings.
It uses:
- A normalization function to lowercase text and replace non‑letters
- Python's split() for tokenizing
- Sets for fast lookup and automatic duplicate removal
- A simple, efficient intersection operation
"""
def normalize(text: str) -> str:
"""
Normalize a string:
- Convert letters to lowercase
- Replace any non-letter with a space
This ensures consistent word comparison.
"""
result = []
for ch in text:
if ch.isalpha():
result.append(ch.lower())
else:
result.append(" ")
return "".join(result)
def extract_words(text: str) -> set[str]:
"""
Extract words from a string.
This function:
- Normalizes the input
- Splits on whitespace
- Filters out empty entries
- Returns a set for fast lookup and automatic duplicate removal
"""
normalized = normalize(text)
parts = normalized.split()
return set(parts)
def find_common_words(a: str, b: str) -> set[str]:
"""
Find common words between two strings.
This function:
- Extracts words from both strings
- Uses set intersection for efficiency
- Returns a new set containing the common words
"""
words_a = extract_words(a)
words_b = extract_words(b)
return words_a & words_b # efficient intersection
def main():
s1 = "The quick brown fox jumps over the lazy dog."
s2 = "A lazy dog sleeps while the quick fox runs away."
common = find_common_words(s1, s2)
print("Common words:")
for w in sorted(common):
print(w)
if __name__ == "__main__":
main()
"""
run:
Common words:
dog
fox
lazy
quick
the
"""
