# Recursive Solution
def letter_by_letter_recursive(word1, word2):
    print(word1)
    if word1 == word2:
        return
    for i,_ in enumerate(word1):
        if word1[i] != word2[i]:
            new_word = word2[:i+1] + word1[i+1:]
            return letter_by_letter_recursive(new_word, word2)
 
 
# Naive Solution
def letter_by_letter_naive(word1, word2):
    print(word1)
    w1, w2 = list(word1), word2
    i = 0
    while w1 != list(w2):
        if w1[i] != w2[i]:
            w1[i] = w2[i]
            print(''.join(w1))
        i += 1
 
 
# Test Cases
print('* * * Recursive Test * * *')
tests = [('floor', 'brake'), ('wood', 'book'), ('a fall to the floor', 'braking the door in')]
for test in tests:
    print('\n{} --> {}'.format(test[0], test[1]))
    letter_by_letter_recursive(test[0], test[1])
 
 
print('\n\n* * * Niave Test * * *')
for test in tests:
    print('\n{} --> {}'.format(test[0], test[1]))
    letter_by_letter_naive(test[0], test[1])

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