Reverse Vowels

Unit 4 Session 1 (Click for link to problem statements)

U-nderstand

Understand what the interviewer is asking for by identifying key aspects of the problem.

• Are we considering both uppercase and lowercase vowels?
  • Yes, both cases should be considered.
• Does the order of consonants need to remain unchanged?
  • Yes, only the vowels should be moved.

P-lan

Plan the solution with pseudocode before coding.

General Idea: Use two pointers to locate vowels from both ends of the string and swap them until they meet.

1) Convert the string into a list to enable in-place swaps.
2) Set up two pointers, one starting at the beginning (`left`) and the other at the end (`right`) of the list.
3) While `left` pointer is less than `right` pointer:
  a) Move `left` pointer rightward until it points to a vowel.
  b) Move `right` pointer leftward until it points to a vowel.
  c) If both pointers point to vowels, swap them and move both pointers towards the center.
4) Join the list back into a string and return.

⚠️ Common Mistakes

• Skipping characters that are vowels due to incorrect condition checks.
• Not preserving the position of consonants.

I-mplement

def make_palindrome(s):
    # Convert the string to a list to modify characters
    chars = list(s)
    left, right = 0, len(s) - 1

    while left < right:
        if chars[left] != chars[right]:
            # Replace the character at the higher index with the smaller of the two
            if chars[left] > chars[right]:
                chars[left] = chars[right]
            else:
                chars[right] = chars[left]
        left += 1
        right -= 1

    # Convert the list back to a string
    return "".join(chars)