We use two pointers l and r at the ends of the string. We skip non-vowel characters and swap the vowels at l and r.

1. Convert string to list s_list.
2. l = 0, r = len(s) - 1.
3. vowels = set("aeiouAEIOU").
4. While l < r:
   • While l < r and s_list[l] not in vowels: l += 1.
   • While l < r and s_list[r] not in vowels: r -= 1.
   • Swap s_list[l] and s_list[r].
   • l += 1, r -= 1.
5. Return ".join(s_list)`.

• Time Complexity: O(N).
• Space Complexity: O(N) (due to list conversion).

def reverse_vowels(s):
    vowels = set("aeiouAEIOU")
    s = list(s)
    l, r = 0, len(s) - 1
    
    while l < r:
        if s[l] not in vowels:
            l += 1
        elif s[r] not in vowels:
            r -= 1
        else:
            s[l], s[r] = s[r], s[l]
            l += 1
            r -= 1
            
    return "".join(s)