LeetCode 125 Valid Palindrome

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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.

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.

题目分析：简单题，头尾指针判断即可，击败60%

public class Solution {        public boolean ok(char ch) {        if (ch >= '0' && ch <= '9') {            return true;        } else if (ch >= 'A' && ch <= 'Z') {            return true;        } else if (ch >= 'a' && ch <= 'z') {            return true;        }        return false;    }        public boolean isPalindrome(String s) {        int len = s.length();        if (len < 2) {            return true;        }        String str = s.toLowerCase();        int i = 0, j = len - 1;        while (i < j) {            while (i < j && !ok(str.charAt(i))) {                i ++;            }               while (i < j && !ok(str.charAt(j))) {                j --;            }            if (str.charAt(i) != str.charAt(j)) {                return false;            }            i ++;            j --;        }        return true;    }}

当然各种调用现成的两行即可实现

public class Solution {        public boolean isPalindrome(String s) {        String str = s.toLowerCase().replaceAll("[^a-z0-9]", "");        return new StringBuffer(str).reverse().toString().equals(str);    }}

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