# 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;
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