Valid Palindrome

本文介绍了一种方法来判断给定字符串中的数字和字母字符组成是否为回文,包括处理空字符串的情况,并提供了一个简单的Java代码实现。

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Given a string, determine if it is a palindrome, considering only alphanumeric

 characters and ignoring cases.

For example,

"A man, a plan, a canal: Panama" is a palindrome.

"race a car" is not a palindrome.

判断一个字符串的数字字母字符组成是否是回文,空字符串是回文。

最简单的方法是将字符串中的飞字母数字字符替换为空字符,两端判断字符相等。

public boolean isPalindrome(String s) {
	s=s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
	for(int i=0;i<s.length()/2;i++){
		if(s.charAt(i)!=s.charAt(s.length()-1-i))
			return false;
	}
	return true;
}


### XTUOJ Perfect Palindrome Problem Analysis For the **Perfect Palindrome** problem on the XTUOJ platform, understanding palindromes and string manipulation algorithms plays a crucial role. A palindrome refers to a word, phrase, number, or other sequences of characters which reads the same backward as forward[^1]. The challenge typically involves checking whether a given string meets specific conditions to be considered a perfect palindrome. In many similar problems, preprocessing steps such as converting all letters into lowercase (or uppercase) can simplify subsequent checks by ensuring case insensitivity during comparison operations. Additionally, removing non-alphanumeric characters ensures that only relevant symbols participate in determining if the sequence forms a valid palindrome[^2]. To determine if a string is a perfect palindrome, one approach iterates from both ends towards the center while comparing corresponding elements until reaching the midpoint without encountering mismatches: ```python def is_perfect_palindrome(s): cleaned_string = ''.join(char.lower() for char in s if char.isalnum()) left_index = 0 right_index = len(cleaned_string) - 1 while left_index < right_index: if cleaned_string[left_index] != cleaned_string[right_index]: return False left_index += 1 right_index -= 1 return True ``` This function first creates `cleaned_string`, stripping away any irrelevant characters and normalizing cases. Then through iteration with two pointers moving inward simultaneously (`left_index` starting at position 0 and `right_index` initially set to the last index), comparisons occur between pairs of opposing positions within the processed input string. If every pair matches perfectly throughout this process, then the original string qualifies as a "perfect palindrome".
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