Longest Palindrome in a String

Programming
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1

Problem Statement

Write a program to find the longest palindrome within a given string.

My Approach

I used Java’s ArrayList collection framework to solve the problem. I iteratively extracted substrings of the given string, and checked if each substring was a palindrome using a separate function. If a substring was determined to be a palindrome, I stored it in the ArrayList. I then sorted the palindromes in the ArrayList using a selection sort algorithm, and printed the longest palindrome.

Code

class Solution {

    public boolean isPalindrome(String check)
    {
        String sum = " ";
        for(int i=check.length()-1;i>=0;i--)
        {
          sum = sum + check.charAt(i);
        }
        if(sum.equalsIgnoreCase(check)==true)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    public String longestPalindrome(String s) {
       ArrayList<String> list = new ArrayList<String>();
        String sum = " ";
        for(int i=0;i<s.length()-1;i++)
        {
          for(int j=i+1;j<s.length();j++)
          {
               sum = s.substring(i,j+1);
          
          if(isPalindrome(sum)==true)
          {
              list.add(sum);
              sum= " ";
          }
          else
          {
              sum=" ";
              continue;
          }
          }
        }

        for(int i = 0;i<list.size()-1;i++)
        {
            int minIndex=i;
            for(int j=i+1;j<list.size();j++)
            {
               if(list.get(j).length()<list.get(minIndex).length())
               {
                   minIndex=j;
               }
            }
            String temp = list.get(i);
            list.add(i, list.get(minIndex));
            list.add(minIndex, temp);
        }

        if(list.size()!=0)
        {

        
        String get = list.get(list.size()-1);
        return get;
        }
        else
        {
            return null;
        }
    }
}
2

The longest palindrome in the given string can be found using the following approach:

class Solution {

    public boolean isPalindrome(String check) {
        String sum = " ";
        for(int i = check.length() - 1; i >= 0; i--) {
            sum = sum + check.charAt(i);
        }
        return sum.equalsIgnoreCase(check);
    }
    
    public String longestPalindrome(String s) {
        ArrayList<String> list = new ArrayList<String>();
        String sum = " ";
        for(int i = 0; i < s.length() - 1; i++) {
            for(int j = i + 1; j < s.length(); j++) {
                sum = s.substring(i, j + 1);
                if(isPalindrome(sum)) {
                    list.add(sum);
                    sum = " ";
                } else {
                    sum = " ";
                    continue;
                }
            }
        }

        for(int i = 0; i < list.size() - 1; i++) {
            int minIndex = i;
            for(int j = i + 1; j < list.size(); j++) {
                if(list.get(j).length() < list.get(minIndex).length()) {
                    minIndex = j;
                }
            }
            String temp = list.get(i);
            list.set(i, list.get(minIndex));
            list.set(minIndex, temp);
        }

        if(list.size() != 0) {
            return list.get(list.size() - 1);
        } else {
            return null;
        }
    }
}

This program will find the longest palindrome within the given string.