missingPermutations

Given a list containing permutations of a set of characters, list all of the missing permutations in lexicographical order.

There can be multiple occurrences of the same permutation in the input. In the output, however, all of the permutations need to be unique.

Examples:

• For permutationList=["ab"], the output should be missingPermutations(permutationList) = ["ba"].

  There are 2 permutations of 'a' and 'b': "ab" and "ba". The only permutation missing from the input is "ba".

• For permutationList=["bca", "bac", "acb"], the output should be
  missingPermutations(permutationList) = ["abc", "cab", "cba"].

  There are 6 permutations of 'a', 'b', and 'c'. The missing permutations, sorted lexicographically, are "abc", "cab" and "cba".

• For permutationList=["a"], the output should be missingPermutations(permutationList) = [].

  The result is empty since "a" is the only permutation of the set of letters consisting of a single letter 'a'.

Input/Output:

• [execution time limit] 1 seconds

• [input] array.string permutationList

  permutationList.length ≥ 1,
  0 ≤ permutationList[i].length ≤ 6,
  permutationList[i].length = permutationList[j].length,
  permutationList[i] contains the same set of distinct characters for each i.

• [output] array.string

  The list of missing permutations sorted in lexicographical order.