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Commit 61eaf8a

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Added solution for the Valid Palindrome problem
Signed-off-by: Krishna Kishore Shetty <kkshetty.work@pm.me>
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‎valid_palindrome/Notes.md

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Original: https://leetcode.com/problems/valid-palindrome/solutions/5056369/simple-2-line-python3-solution-beats-91-on/
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# Intuition
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We simply remove the unwanted characters from the string, convert to lowercase, and reverse the string and then compare to the original.
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# Approach
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- Import the Python Regex module
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- Convert input string to lowercase
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- Use it remove the unwanted characters, which are all characters excluding letters and numbers
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- Now that we have the *cleaned* input string, compare it to the reversed version of itself, and return the result.
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# Complexity
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- Time complexity:
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$$O(n)$$
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Note: This excludes the time taken by the Python Regex module(`re`) to match and substitute the unwanted characters from the input string.
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This [StackOverflow answer](https://stackoverflow.com/a/21702/2627137) says its $$O(2^m + n)$$, where m is length of regex string, and n is length of input string
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Reversing the string is an O(n) operation. And so is string comparison.
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Therefore overall complexity exhibits linear growth along with size of input.
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- Space complexity:
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$$O(n)$$
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# Code
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```python
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import re
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class Solution:
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def isPalindrome(self, s: str) -> bool:
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s_clean = re.sub('[^a-z0-9]','',s.lower())
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return s_clean==s_clean[::-1]
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```

‎valid_palindrome/Solution.py

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import re
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class Solution:
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def isPalindrome(self, s: str) -> bool:
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s_clean = re.sub('[^a-z0-9]','',s.lower())
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return s_clean==s_clean[::-1]

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