Valid Palindrome

最新推荐文章于 2024-01-04 12:53:14 发布

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本文介绍了一种方法来判断给定的字符串是否为回文，仅考虑字母数字字符并忽略大小写。通过双指针技术从两端向中间遍历字符串，跳过非字母数字字符进行比较。

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.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

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

public class Solution {

	public  boolean isalphanumeric (char c){
		if(c>='0'&&c<='9'||c>='a'&&c<='z'||c>='A'&&c<='Z'){
			return true;
		}
		return false;
	}
	
	public boolean isPalindrome(String s) {
        
		if(s==null||s.length()==0)return true;
		int i = 0;
		int j = s.length()-1;
		while(i<j){
			while(i<j&&!isalphanumeric(s.charAt(i))){
				i++;
			}
			while(i<j&&!isalphanumeric(s.charAt(j))){
				j--;
			}
			if(Character.toLowerCase(s.charAt(i))!=Character.toLowerCase(s.charAt(j))){
				return false;
			}
			i++;j--;
		}
		return true;
    }
	
	public static void main(String [] args){
		Solution solution = new Solution();
		String str1 = new String("A man, a plan, a canal: Panama");
		String str2 = new String("race a car");
		System.out.println(solution.isPalindrome(str1));
		System.out.println(solution.isPalindrome(str2));
	}
}