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Palindrome Check

Certification: Basic Level Accuracy: 67.27% Submissions: 55 Points: 5

Write a Java program to implement the isPalindrome(String s) function, which checks if a string is a palindrome by considering only alphanumeric characters and ignoring case.

Example 1
    

  • Input: s = "A man, a plan, a canal: Panama"
    • 

  • Output: true
    • 

  • Explanation:

      

    • Cleaned string = "amanaplanacanalpanama"
      • 

    • Same forwards and backwards → true
      • 

    

    •
Example 2
    

  • Input: s = "race a car"
    • 

  • Output: false
    • 

  • Explanation:

      

    • Cleaned string = "raceacar"
      • 

    • Reverse = "racaecar" → not same → false
      • 

    

    •
Constraints
    

  • 1 ≤ s.length ≤ 2 * 10^5
    • 

  • The string consists of ASCII characters
    • 

  • Time Complexity: O(n)
    • 

  • Space Complexity: O(1)
    •
StringsEYPhillips
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Hint
Solution

Solution Hints

    
  
  • Clean the string by removing non-alphanumeric characters and converting to lowercase
    • 
  
  • Use two pointers, one at the start and one at the end of the cleaned string
    • 
  
  • Compare characters at both pointers
    • 
  
  • Move the pointers toward the center
    • 
  
  • If any characters don't match, the string is not a palindrome
    •

Steps to solve by this approach:

 Step 1: Initialize two pointers, left at the start of the string (index 0) and right at the end (index length-1).
 Step 2: Skip non-alphanumeric characters by moving the left pointer to the right.
 Step 3: Skip non-alphanumeric characters by moving the right pointer to the left.
 Step 4: Compare the characters at the left and right pointers (ignoring case).
 Step 5: If the characters don't match, return false.
 Step 6: Move the pointers toward the center (increment left, decrement right).
 Step 7: If all characters match until the pointers meet or cross, return true.

Submitted Code :