Alphabetically output substrings

alphabetical-substring.cpp

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <unordered_set>

using namespace std;

void printSubstring(string s, vector<string> substrings) {
    if (substrings.empty()) return;
    unordered_set<string> exist;
    sort(substrings.begin(), substrings.end());
    for (string sub : substrings) {
        for (int i = 1; i <= sub.size(); i++) {
            string output = sub.substr(0, i);
            if (exist.find(output) == exist.end()) {
                exist.insert(output);
                cout << output << endl;
            }
        }
    }
}

void alphabeticalSubstring(string s) {
    if (s.empty()) return;
    if (s.size() == 1) {
        cout << s << endl;
        return;
    }
    vector<vector<string>> substringMap(26, vector<string>());
    for (int i = 0; i < s.size(); i++) {
        if (s[i] >= 'A' && s[i] <= 'Z') substringMap[s[i]-'A'].push_back(s.substr(i));
        if (s[i] >= 'a' && s[i] <= 'z') substringMap[s[i]-'a'].push_back(s.substr(i));
    }
    for (int i = 0; i < 26; i++) printSubstring(s, substringMap[i]);
}

int main(int argc, char* argv[]) {
    if (argc != 2) {
        cout << "Input one string as parameter" << endl;
        return 1;
    }
    alphabeticalSubstring(string(argv[1]));
    return 0;
}