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validPalin.java
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66 lines (55 loc) · 1.91 KB
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class validPalin {
public static boolean isPalindrome(String s) {
// convert to lower case
s = s.toLowerCase();
// build a string with solely char or dig
StringBuilder sb = new StringBuilder();
for (char elem : s.toCharArray()) {
if (Character.isLetterOrDigit(elem)) {
sb.append(elem);
}
}
String alNumString = sb.toString(); // redundant
int r = alNumString.length() - 1;
int l = 0;
while (r > l) {
if (alNumString.charAt(l) != alNumString.charAt(r)) {
return false;
}
r--;
l++;
}
return true;
}
public static void main(String[] args) {
String s1 = "A man, a plan, a canal: Panama";
System.out.println("Output1: " + isPalindrome(s1));
String s2 = "race a car";
System.out.println("Output2: " + isPalindrome(s2));
String s3 = " ";
System.out.println("Output3: " + isPalindrome(s3));
}
}
/*
https://leetcode.com/problems/valid-palindrome/description/
start at both ends; each element must equal each other after downcase and
if alphanumeric
* 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.
*/