Missing Alphabets

Adriana was playing with the English alphabet. When she was done playing with the alphabet, she realized that she had jumbled up the positions of the letters. Now, given a set of words, she wondered what would be the dictionary ordering of these words based on the new alphabet ordering which she made.

In other words, given a permutation of the English alphabet, E, and a set of words S, you need to output the lexicographical ordering of the words in the set S based on the new alphabet, E.

Example:

Input:  s = "abcdefghijklmnopqrstuvwxyz", m = 2, v = {"aa", "bb"}

Output:

aa
bb

Approach:

C++

#include <bits/stdc++.h>
using namespace std;

unordered_map<char, int> ump;
bool cmp(string a, string b)
{
    for (int i = 0; i < min(a.size(), b.size()); i++)
    {
        if (ump[a[i]] == ump[b[i]])
            continue;
        return ump[a[i]] < ump[b[i]];
    }
    return a.size() < b.size();
}

void missingAlphabets(string s, vector<string> &v, int m)
{
    ump.clear();
    for (int i = 0; i < s.size(); i++)
        ump[s[i]] = i;
    sort(v.begin(), v.end(), cmp);
    for (int i = 0; i < m; i++)
        cout << v[i] << "\n";
}
int main()
{

    string s = "abcdefghijklmnopqrstuvwxyz";

    int m = 2;
    vector<string> v = {"aa", "bb"};

    missingAlphabets(s, v, m);

    return 0;
}