题解

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>

using namespaceace std;

map<int, vector<char>> digitMap = {
    {2, {'a', 'b', 'c'}},
    {3, {'d', 'e', 'f'}},
    {4, {'g', 'h', 'i'}},
    {5, {'j', 'k', 'l'}},
    {6, {'m', 'n', 'o'}},
    {7, {'p', 'q', 'r', 's'}},
    {8, {'t', 'u', 'v'}},
    {9, {'w', 'x', 'y', 'z'}}
};

vector<string> com;

void genCom(vector<int>& digits, int index, string current) {
    if (index == digits.size()) {
        com.push_back(current);
        return;
    }
    
    int digit = digits[index];
    vector<char>& letters = digitMap[digit];
    
    for (char letter : letters) {
        genCom(digits, index + 1, current + letter);
    }
}

int main() {
    int N;
    cin >> N;
    
    vector<int> digits(N);
    for (int i = 0; i < N; i++) {
        cin >> digits[i];
    }
    
    genCom(digits, 0, "");
    
    sort(com.begin(), com.end());
    
    int M = com.size();
    cout << M << endl;
    
    for (string com : com) {
        cout << com << endl;
    }
    
    return 0;
}