/**
* Source : https://oj.leetcode.com/problems/valid-palindrome/
*
*
* 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 ValidPalindrome {
/**
* 判断一个字符串是否是回文字符串，只判断字符串里面的字母和数字
*
* @param str
* @return
*/
public boolean valid (String str) {
int left = 0;
int right = str.length()-1;
while (left <= right) {
// 过滤左边非数字字母
while (left < str.length() && !isAlphanumeric(str.charAt(left))) {
left++;
}
// 过滤右边非数字字母
while (0 < right && !isAlphanumeric(str.charAt(right))) {
right--;
}
if (left >= right) {
return true;
}
if (Character.toLowerCase(str.charAt(left++)) != Character.toLowerCase(str.charAt(right--))) {
return false;
}
}
return true;
}
public boolean isAlphanumeric (char c) {
if ((c >= 48 && c <= 57) || ((c >= 65 && c <= 90) || (c >= 97 && c<= 122))) {
return true;
}
return false;
}
public static void main(String[] args) {
ValidPalindrome validPalindrome = new ValidPalindrome();
System.out.println(validPalindrome.valid("A man, a plan, a canal: Panama") + "-----true");
System.out.println(validPalindrome.valid("race a car") + "-----false");
}
}