LeetCode: 125. Valid Palindrome

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125. Valid Palindrome

LeetCode - Valid Palindrome

基本思路就是从两边想中间挤压。记得前不久有一道题使用了相似的处理手段，容我有时间找找看！

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

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/**
 * Runtime: 3 ms, faster than 96.33% of Java online submissions for Valid Palindrome.
 *
 * Memory Usage: 38.3 MB, less than 76.78% of Java online submissions for Valid Palindrome.
 */
public boolean isPalindrome(String s) {
    if (Objects.isNull(s) || s.length() == 0) {
        return true;
    }
    int left = 0;
    int right = s.length() - 1;
    while (left <= right) {
        char lc = s.charAt(left);
        char rc = s.charAt(right);
        if (!isAlphanumberic(lc)) {
            left++;
        } else if (!isAlphanumberic(rc)) {
            right--;
        } else {
            if (Character.toLowerCase(lc) != Character.toLowerCase(rc)) {
                return false;
            }
            left++;
            right--;
        }
    }
    return true;
}

private boolean isAlphanumberic(char aChar) {
    return ('a' <= aChar && aChar <= 'z') || ('A' <= aChar && aChar <= 'Z')
            || ('0' <= aChar && aChar <= '9');
}