125. Valid Palindrome
Tags: ‘Two Pointers’, ‘String’
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example 1:
Input: "A man, a plan, a canal: Panama" Output: true
Example 2:
Input: "race a car" Output: false
Solution
O(n) time O(1) space 82% 96%
// BETTER
public boolean isPalindrome(String s) {
if (s == null || s.length() <= 1) {
return true;
}
int i = 0, j = s.length() - 1;
while (i < j) {
if (!Character.isLetterOrDigit(s.charAt(i))) {
i++;
} else if (!Character.isLetterOrDigit(s.charAt(j))) {
j--;
} else {
if (Character.toLowerCase(s.charAt(i)) != Character.toLowerCase(s.charAt(j))) {
return false;
}
i++;
j--;
}
}
return true;
}
public boolean isPalindrome(String s) {
if (s == null || s.length() <= 1) {
return true;
}
for (int i = 0, j = s.length() - 1; i < j; i++, j--) {
while (!Character.isLetterOrDigit(s.charAt(i)) && i < j) {
i++;
}
while (!Character.isLetterOrDigit(s.charAt(j)) && j > i) {
j--;
}
if (Character.toLowerCase(s.charAt(i)) != Character.toLowerCase(s.charAt(j))) {
return false;
}
}
return true;
}