LeetCode – Pares Palindrome (Java)

public List<List<Integer>> palindromePairs(String[] words) {
    List<List<Integer>> result = new ArrayList<>();
    if(words == null || words.length < 2){
        return result;
    }
 
    HashMap<String, Integer> map = new HashMap<>();
    for(int i=0; i<words.length; i++){
        map.put(words[i], i);
    }
 
    for(int i=0; i<words.length; i++){
        String s = words[i];
 
        for(int k=0; k<=s.length(); k++){
            String left = s.substring(0, k);
            String right= s.substring(k);
 
            //if left part is palindrome, find reversed right part
            if(isPalindrome(left)){
                String reversedRight = new StringBuilder(right).reverse().toString();
                if(map.containsKey(reversedRight) && map.get(reversedRight) != i){
                    ArrayList<Integer> l = new ArrayList<>();
                    l.add(map.get(reversedRight));
                    l.add(i);
                    result.add(l);
                }
            }
 
            //if right part is a palindrome, find reversed left part
            if(isPalindrome(right)){
                String reversedLeft = new StringBuilder(left).reverse().toString();
                if(map.containsKey(reversedLeft) 
                        && map.get(reversedLeft) != i 
                        && right.length() != 0){ 
                        //make sure right is not "", already handled in the if above
                    ArrayList<Integer> l = new ArrayList<>();
                    l.add(i);
                    l.add(map.get(reversedLeft));
                    result.add(l);
                }
            }
        }
    }
 
    return result;
}
 
public boolean isPalindrome(String s){
    int i=0;
    int j=s.length()-1;
 
    while(i<=j){
        if(s.charAt(i)!=s.charAt(j)){
            return false;
        }
        i++;
        j--;
    }
 
    return true;
}