# 125 Valid Palindrome – Easy

### Problem:

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.

### Thoughts:

This is just a very basic string manipulation problem. Iteration of String.

### Solutions:

``````public class Solution {
public boolean isPalindrome(String s) {
if (s == null || s.equals("")){
return true;
}
s = s.toLowerCase();
s = s.replaceAll("[^A-Za-z0-9]","");
int i = 0;
int j = s.length() -1;
for (; i < j; i ++, j --){
if (s.charAt(i) != s.charAt(j)){
return false;
}
}
return true;
}//isPalindrome
}
``````

Updated: 11/28/2016 Alternative solution:

``````public class Solution {
public boolean isPalindrome(String s) {
s = s.toLowerCase();
boolean result = true;
int i = 0, j = s.length() - 1;
while (i < j) {
if (!((s.charAt(i) >= 'a' && s.charAt(i) <= 'z') || (s.charAt(i) >= '0' && s.charAt(i) <= '9'))) {
i ++;
continue;
}
if (!((s.charAt(j) >= 'a' && s.charAt(j) <= 'z') || (s.charAt(j) >= '0' && s.charAt(j) <= '9'))) {
j --;
continue;
}
if (s.charAt(i) != s.charAt(j)) {
result = false;
break;
}
i ++;
j --;
}
return result;
}
}
``````