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Palindrome.java

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package Others;

class Palindrome {

private String reverseString(String x) { // *helper method

StringBuilder output = new StringBuilder(x);

return output.reverse().toString();

}

public boolean FirstWay(String x) { // *palindrome method, returns true if palindrome

if (x == null || x.length() <= 1)

return true;

return x.equalsIgnoreCase(reverseString(x));

}

public boolean SecondWay(String x) {

if (x.length() == 0 || x.length() == 1)

return true;

if (x.charAt(0) != x.charAt(x.length() - 1))

return false;

return SecondWay(x.substring(1, x.length() - 1));

}

/**

* This method ignores all non-alphanumeric characters and case runs in O(n)

* where n is the length of s

*

* @param s String to check

* @return true if s is palindrome else false

*/

public boolean isPalindrome(String s) {

s = s.toLowerCase().trim();

StringBuilder sb = new StringBuilder();

for (char c : s.toCharArray()) {

if (Character.isLetter(c) || Character.isDigit(c))

sb.append(c);

}

s = sb.toString();

int start = 0;

int end = s.length() - 1;

while (start <= end) {

if (s.charAt(start++) != s.charAt(end--))

return false;

}

return true;

}

}