Two strings X and Y are similar if we can swap two letters (in different positions) of X, so that it equals Y. Also two strings X and Y are similar if they are equal. For example, "tars " and "rats " are similar (swapping at positions 0 and 2), and "rats " and "arts " are similar, but "star " is not similar to "tars ", "rats ", or "arts ". Together, these form two connected groups by similarity: { "tars ", "rats ", "arts "} and { "star "}. Notice that "tars " and "arts " are in the same group even though they are not similar. Formally, each group is such that a word is in the group if and only if it is similar to at least one other word in the group.