Compare two Maps and remove all the elements that either have the same key or the same value

I have two Maps that I need to compare and merge them into a result map. I need to remove all the elements that either have the same key or the same value.

Basically, say I have two Maps:

Map<String, String> map1 = new HashMap<>();
map1.put("1", "A");
map1.put("2", "A");
map1.put("3", "B");
map1.put("4", "C");
map1.put("5", "D");
map1.put("6", "E");

Map<String, String> map2 = new HashMap<>();
map2.put("1", "B");
map2.put("2", "A");
map2.put("4", "F");
map2.put("6", "C");
map2.put("7", "G");
map2.put("8", "H");

I need to remove all the entries that have either the same keys or the same values and need to retain back only bidirectional unique entries. So after merge, I need to have the following result map in which every key maps to a unique value and every value has a unique key:

("5", "D"), ("7", "G"), ("8", "H")

What's the best way to do this in Java?