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

Understand what the interviewer is asking for by using test cases and questions about 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.

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Identify vowels using a helper function, then use two pointers to swap the vowels from both ends towards the middle.

1) Define a helper function `is_vowel` to check if a character is a vowel. 2) Convert the string to a list for in-place modifications. 3) Initialize two pointers, `left` at the beginning and `right` at the end of the list. 4) While `left` pointer is less than `right` pointer: a) Increment `left` until it points to a vowel. b) Decrement `right` until it points to a vowel. c) Swap the characters at `left` and `right`. d) Move both `left` and `right` inward to continue the process. 5) Convert the list back to a string and return.

⚠️ Common Mistakes

• Skipping characters that are vowels due to incorrect condition checks.
• Incorrect handling of the two pointers can cause an infinite loop or early termination of the function.

def is_vowel(c): # Check if a character is a vowel (considering both lowercase and uppercase) return c in 'aeiouAEIOU' def reverse_vowels(s): # Convert the string to a list to modify it in place s_list = list(s) left = 0 right = len(s) - 1 while left < right: # Move the left pointer until it points to a vowel while left < right and not is_vowel(s_list[left]): left += 1 # Move the right pointer until it points to a vowel while left < right and not is_vowel(s_list[right]): right -= 1 # Swap the vowels temp = s_list[left] s_list[left] = s_list[right] s_list[right] = temp left = left + 1 right = right - 1 # Convert the list back into a string return ''.join(s_list)