A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.
Given a string s, return true if it is a palindrome, or false otherwise.
Example 1:
Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.
Example 2:
Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.
Example 3:
Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.
Constraints:
- 1 <= s.length <= 2 * 10^5
- s consists only of printable ASCII characters.
Solution
class Solution {
public boolean isPalindrome(String s) {
int lo = 0;
int hi = s.length() - 1;
while (lo < hi) {
char loChar = s.charAt(lo);
if (!Character.isLetterOrDigit(loChar)) {
lo++;
continue;
}
char hiChar = s.charAt(hi);
if (!Character.isLetterOrDigit(hiChar)) {
hi--;
continue;
}
loChar = Character.isUpperCase(loChar)? Character.toLowerCase(loChar): loChar;
hiChar = Character.isUpperCase(hiChar)? Character.toLowerCase(hiChar): hiChar;
if (loChar == hiChar) {
lo++;
hi--;
continue;
} else {
return false;
}
}
return true;
}
}
Solution 2021-01-30
class Solution {
public boolean isPalindrome(String s) {
int lo = 0;
int hi = s.length() - 1;
while (lo < hi) {
char left = s.charAt(lo);
char right = s.charAt(hi);
if (!Character.isLetterOrDigit(left)) {
lo++;
continue;
}
if (!Character.isLetterOrDigit(right)) {
hi--;
continue;
}
if (Character.isUpperCase(left)) {
left = Character.toLowerCase(left);
}
if (Character.isUpperCase(right)) {
right = Character.toLowerCase(right);
}
if (left != right) {
return false;
}
lo++;
hi--;
}
return true;
}
}