[LeetCode 125] Valid Palindrome

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Description

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A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.

Example 1

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• Input: s = “A man, a plan, a canal: Panama”
• Output: true
• Explanation: “amanaplanacanalpanama” is a palindrome.

Example 2

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• Input: s = “race a car”
• Output: false
• Explanation: “raceacar” is not a palindrome.

Example 3

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• Input: s = “ “
• Output: true
• Explanation:
  • s is an empty string “” after removing non-alphanumeric characters.
  • Since an empty string reads the same forward and backward, it is a palindrome.

Constraints

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• 1 <= s.length <= 2 * 10^5
• s consists only of printable ASCII characters.

Code

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내 제출

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

Runtime	Memory
2 ms	43.3 MB

다른 풀이

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 class Solution {

    public boolean isPalindrome(String s) {

        s = s.toLowerCase();
        s = s.replaceAll("[^a-z0-9]", "");

        int left = 0;
        int right = s.length() - 1;

        while (left < right) {

            if (s.charAt(left++) != s.charAt(right--)) 
                return false;
        }

        return true;
    }
}

Reference

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• https://github.com/doocs/leetcode/blob/main/solution/0100-0199/0125.Valid%20Palindrome/Solution.java