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Valid Palindrome

Certification: Basic Level Accuracy: 0% Submissions: 0 Points: 5

Write a C program to determine if a string is a palindrome, considering only alphanumeric characters and ignoring cases. A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward (ignoring spaces, punctuation, and capitalization). The function should return true if the string is a palindrome and false otherwise.

Example 1
    
  
  • Input: s = "A man, a plan, a canal: Panama"
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  • Output: true
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  • Explanation: After filtering out non-alphanumeric characters and converting to lowercase: "amanaplanacanalpanama". This reads the same backward as forward, making it a palindrome.
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Example 2
    
  
  • Input: s = "race a car"
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  • Output: false
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  • Explanation: After filtering out non-alphanumeric characters and converting to lowercase: "raceacar". This does not read the same backward as forward, so it's not a palindrome.
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Constraints
    
  
  • 1 ≤ s.length ≤ 2 * 10^5
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  • s consists only of printable ASCII characters
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  • Time Complexity: O(n) where n is the length of the string
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  • Space Complexity: O(1) as we're doing it in-place
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StringsGoldman SachsTutorix
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Hint
Solution

Solution Hints

    
  
  • Use two pointers technique, one starting from the beginning and one from the end
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  • Skip non-alphanumeric characters
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  • Convert each character to lowercase before comparison
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  • Compare characters from both ends moving inward
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  • Return false if any comparison fails, otherwise return true
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Steps to solve by this approach:

 Step 1: Initialize two pointers, left starting at the beginning of the string and right starting at the end.

 Step 2: Move the left pointer forward while the current character is not alphanumeric.

 Step 3: Move the right pointer backward while the current character is not alphanumeric.

 Step 4: Compare the characters at both pointers after converting them to lowercase.

 Step 5: If the characters don't match, return false immediately.

 Step 6: Move the left pointer forward and the right pointer backward.

 Step 7: Repeat until the pointers meet or cross each other. If we reach this point without returning false, the string is a palindrome.

Submitted Code :