public static boolean buddyStrings(String A, String B) {

if (A.length() != B.length() || A.length() <= 1 || B.length() <= 1) {

return false;

}

if (A.equals(B)) {

Set<Character> s = new HashSet<Character>();

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

s.add(c);

}

return s.size() < A.length();

}

List<Integer> dif = new ArrayList<>();

for (int i = 0; i < A.length(); ++i) {

if (A.charAt(i) != B.charAt(i)) {

dif.add(i);

}

}

return dif.size() == 2 && A.charAt(dif.get(0)) == B.charAt(dif.get(1)) && A.charAt(dif.get(1)) == B.charAt(dif.get(0));

}