LeetCode - Algorithms - 125. Valid Palindrome

Problem

125. Valid Palindrome

Java

Two pointers

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class Solution {
    public boolean isPalindrome(String s) {
        final int N = s.length();
        char c1, c2;
        for (int i = 0, j = N - 1; i < j; ) {
            c1 = s.charAt(i);
            c2 = s.charAt(j);
            if (!Character.isLetterOrDigit(c1))
                i++;
            else if (!Character.isLetterOrDigit(c2))
                j--;
            else if (Character.toLowerCase(c1) != Character.toLowerCase(c2)) {
                return false;
            } else {
                i++;
                j--;
            }
        }
        return true;
    }
}

Submission Detail

  • 481 / 481 test cases passed.
  • Runtime: 2 ms, faster than 98.05% of Java online submissions for Valid Palindrome.
  • Memory Usage: 39 MB, less than 5.64% of Java online submissions for Valid Palindrome.

alphanumeric and binary

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class Solution {
    public boolean isPalindrome(String s) {
        s = s.replaceAll("[^A-Za-z0-9]", "").toLowerCase();
        int N = s.length();
        for (int i = 0; i < N / 2; i++)
            if (s.charAt(i) != s.charAt(N - 1 - i))
                return false;
        return true;        
    }
}

Submission Detail

  • 480 / 480 test cases passed.
  • Runtime: 883 ms, faster than 12.58% of Java online submissions for Valid Palindrome.
  • Memory Usage: 47.3 MB, less than 18.43% of Java online submissions for Valid Palindrome.

JavaScript

Algorithms, 4th Edition

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/**
 * @param {string} s
 * @return {boolean}
 */
var isPalindrome = function(s) {
    let str = s.toLowerCase().replace(/[^a-zA-Z0-9]/g, "");
    const N = str.length;
    for (let i = 0; i < N / 2; i++) {
        if (str.charAt(i) != str.charAt(N - 1 - i))
            return false;
    }
    return true;    
};

Submission Detail

  • 480 / 480 test cases passed.
  • Runtime: 67 ms, faster than 96.43% of JavaScript online submissions for Valid Palindrome.
  • Memory Usage: 44.2 MB, less than 82.85% of JavaScript online submissions for Valid Palindrome.

Two pointers

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/**
 * @param {string} s
 * @return {boolean}
 */
var isPalindrome = function(s) {
    const N = s.length;
    const ALPHANUMERIC = /^[a-z0-9]+$/i;
    let c1, c2;
    for (let i = 0, j = N - 1; i < j; ) {
        c1 = s.charAt(i);
        c2 = s.charAt(j);
        if (!ALPHANUMERIC.test(c1))
            i++;
        else if (!ALPHANUMERIC.test(c2))
            j--;
        else if (c1.toLowerCase() != c2.toLowerCase()) {
            return false;
        } else {
            i++;
            j--;
        }
    }
    return true;    
};

Submission Detail

  • 480 / 480 test cases passed.
  • Runtime: 102 ms, faster than 45.96% of JavaScript online submissions for Valid Palindrome.
  • Memory Usage: 44.9 MB, less than 61.23% of JavaScript online submissions for Valid Palindrome.