Common Words in Two Strings in Python

Finding common words between two strings is a frequent programming task. This involves splitting strings into words, handling case-insensitivity, and finding intersections between word sets.

For example, if we have s0 = "i love python coding" and s1 = "coding in python is easy", the common words are python and coding, so the count is 2.

Algorithm Steps

To find common words between two strings, follow these steps:

• Convert both strings to lowercase for case-insensitive comparison
• Split each string into a list of words using split()
• Convert word lists to sets and find their intersection
• Return the count of common words

Using Set Intersection

The most efficient approach uses Python sets to find common elements ?

def find_common_words(s0, s1):
    s0 = s0.lower()
    s1 = s1.lower()
    s0_words = s0.split()
    s1_words = s1.split()
    return len(set(s0_words) & set(s1_words))

# Test the function
s0 = "i love python coding"
s1 = "coding in python is easy"
result = find_common_words(s0, s1)
print(f"Number of common words: {result}")

# Show the actual common words
common_words = set(s0.lower().split()) & set(s1.lower().split())
print(f"Common words: {list(common_words)}")

Number of common words: 2
Common words: ['python', 'coding']

Using Class-Based Approach

Here's the object-oriented version of the solution ?

class WordComparator:
    def count_common_words(self, s0, s1):
        s0 = s0.lower()
        s1 = s1.lower()
        s0_words = s0.split()
        s1_words = s1.split()
        return len(set(s0_words) & set(s1_words))
    
    def get_common_words(self, s0, s1):
        s0 = s0.lower()
        s1 = s1.lower()
        s0_words = set(s0.split())
        s1_words = set(s1.split())
        return list(s0_words & s1_words)

# Example usage
comparator = WordComparator()
s0 = "i love python coding"
s1 = "coding in python is easy"

count = comparator.count_common_words(s0, s1)
words = comparator.get_common_words(s0, s1)

print(f"Count: {count}")
print(f"Words: {words}")

Count: 2
Words: ['python', 'coding']

Handling Multiple Test Cases

Let's test with different string combinations ?

def find_common_words_count(s0, s1):
    s0_words = set(s0.lower().split())
    s1_words = set(s1.lower().split())
    return len(s0_words & s1_words)

# Test cases
test_cases = [
    ("i love python coding", "coding in python is easy"),
    ("Hello World", "world hello"),
    ("Python Java C++", "JavaScript Python Ruby"),
    ("no common", "different words")
]

for s0, s1 in test_cases:
    count = find_common_words_count(s0, s1)
    common = set(s0.lower().split()) & set(s1.lower().split())
    print(f"'{s0}' & '{s1}' ? {count} common words: {list(common)}")

'i love python coding' & 'coding in python is easy' ? 2 common words: ['python', 'coding']
'Hello World' & 'world hello' ? 2 common words: ['world', 'hello']
'Python Java C++' & 'JavaScript Python Ruby' ? 1 common words: ['python']
'no common' & 'different words' ? 0 common words: []

Key Points

• Case Insensitive: Use lower() to handle different cases
• Set Operations: Sets provide efficient intersection operations
• Split Method: split() without arguments handles multiple spaces automatically
• Intersection Operator: & finds common elements between sets

Conclusion

Finding common words between strings involves converting to lowercase, splitting into words, and using set intersection. The & operator efficiently finds common elements between two sets of words.