Missing Permutations in a list in C++

Problem statement

Given a list of permutations of any word. Find the missing permutation from the list of permutations.

Example

If permutation is = { “ABC”, “ACB”, “BAC”, “BCA”} then missing
permutations are {“CBA” and “CAB”}

Algorithm

• Create a set of all given strings
• And one more set of all permutations
• Return difference between two sets

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
void findMissingPermutation(string givenPermutation[], size_t
permutationSize) {
   vector<string> permutations;
   string input = givenPermutation[0];
   permutations.push_back(input);
   while (true) {
      string p = permutations.back();
      next_permutation(p.begin(), p.end());
      if (p == permutations.front())
         break;
      permutations.push_back(p);
   }
   vector<string> missing;
   set<string> givenPermutations(givenPermutation,
   givenPermutation + permutationSize);
   set_difference(permutations.begin(), permutations.end(),
      givenPermutations.begin(),
      givenPermutations.end(),
      back_inserter(missing));
   cout << "Missing permutations are" << endl;
   for (auto i = missing.begin(); i != missing.end(); ++i)
      cout << *i << endl;
}
int main() {
   string givenPermutation[] = {"ABC", "ACB", "BAC", "BCA"};
   size_t permutationSize = sizeof(givenPermutation) / sizeof(*givenPermutation);
   findMissingPermutation(givenPermutation, permutationSize);
   return 0;
}

When you compile and execute above program. It generates following output −

Output

Missing permutations are
CAB
CBA