Valid Palindrome LeetCode Solution

The LeetCode problem “Valid Palindrome” (problem 125) requires determining if a given string reads the same forwards and backward, after removing non-alphanumeric characters and converting to lowercase. A naive character-by-character comparison scales linearly with string length, but can be inefficient for very large inputs.

Why This Matters

Real-world string processing often involves validation and transformation steps before comparison. Idealized algorithms assume clean data, but production systems must handle messy, real-world input. Failure to account for this can lead to incorrect results or performance bottlenecks, especially when dealing with user-generated content or large datasets.

Key Insights

LeetCode Problem 125: This problem is a common interview question testing string manipulation skills.
Two-Pointer Approach: Utilizing two pointers, one at the beginning and one at the end of the string, allows for efficient comparison, reducing the time complexity to O(n).
Character Filtering: Ignoring non-alphanumeric characters is a crucial step in real-world string validation scenarios.

Working Example

class Solution {
public boolean isPalindrome(String s) {
s = s.toLowerCase();
int left = 0;
int right = s.length() - 1;
while (left < right) {
char chLeft = s.charAt(left);
char chRight = s.charAt(right);
if (!(chLeft >= 'a' && chLeft <= 'z' || chLeft >= '0' && chLeft <= '9')) {
left++;
continue;
}
if (!(chRight >= 'a' && chRight <= 'z' || chRight >= '0' && chRight <= '9')) {
right--;
continue;
}
if (chLeft != chRight) {
return false;
}
left++;
right--;
}
return true;
}
}

Practical Applications

Data Validation: Systems like search engines use palindrome checks (and more complex string analysis) to identify and filter invalid or malicious input.
Pitfall: Ignoring case sensitivity can lead to false positives; always convert to lowercase or uppercase before comparison.

References:

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Valid Palindrome LeetCode Solution