Repeated strings can be removed by using an associated array (like a balanced binary search tree or a hash map).

The problem can be solved by enumerating \((i,j)\) using a for statement, and inserting the concatenation of the strings \(S _ i\) and \(S _ j\) into an associated array.

The following is sample code.

Sample code in C++

#include <iostream>
#include <vector>
#include <set>
using namespace std;

int main() {
    int N;
    cin >> N;
    vector<string> S(N);
    for (auto&& s : S)
        cin >> s;

    // Use `std::set` to remove duplicating strings
    set<string> ans;
    for (const auto& s : S)
        for (const auto& t : S)
            if (s != t) // If two strings are different
                ans.emplace(s + t); // concatenate them and insert

    // The answer is the size of the set
    cout << size(ans) << endl;
    return 0;
}

Sample code in Python

N = int(input())

S = [input() for i in range(N)]

# Use `set` to remove duplicating strings
ans = set()
for s in S:
    for t in S:
        if s != t: # If two strings are different
            ans.add(s + t) # concatenate them and insert

# The answer is the size of the set
print(len(ans))