Lecture 73 :- Reverse Vowels Of A String

To reverse the vowels of a string means to swap the positions of all the vowel characters in the string while keeping the non-vowel characters in their original places. Here's a Python function that accomplishes this:

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def reverse_vowels(s):    vowels = set("aeiouAEIOU")    s = list(s)    left, right = 0, len(s) - 1    while left < right:        while left < right and s[left] not in vowels:            left += 1        while left < right and s[right] not in vowels:            right -= 1        if left < right:            s[left], s[right] = s[right], s[left]            left += 1            right -= 1    return "".join(s) # Example usage: input_str = "hello" print(reverse_vowels(input_str))  # Output: "holle"

In this function, we first create a set of vowel characters for efficient membership testing. We then convert the input string into a list of characters to make it easier to swap elements. We use two pointers, left and right, which initially point to the first and last characters of the string, respectively.

We iterate through the string from both ends towards the center until the left pointer is less than the right pointer. If we find a vowel at both the left and right positions, we swap them. If one or both of the positions do not contain a vowel, we move the pointers accordingly.

This algorithm has a time complexity of O(N), where N is the length of the input string, as we process each character of the string once. Note that the input string is converted to a list, which takes additional space, but we convert it back to a string before returning the result.