@jinxonik / UniLecs #268

phone_decipher.cpp

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

using std::cout;
using std::endl;
using std::string;
using std::vector;

class PhoneDecipher
{
public:
  void decipher(const string& digits, vector<string>& result);
private:
  void decipher_impl(size_t pos);
  string const* m_digits;
  string m_current;
  vector<string>* m_result;
};

// Make list of strings
void PhoneDecipher::decipher(const string& digits, vector<string>& result)
{
  result.clear();                   // clear list of resulting string list
  if (digits.size() == 0) { return; }
  m_digits = &digits;               // to reduce stack usage
  m_current.resize(digits.size());  // string for local result (no extra strings are required)
  m_result = &result;               // to reduce stack usage
  decipher_impl(0);
}

// Implementation (for internal use)
void PhoneDecipher::decipher_impl(size_t pos)
{
  unsigned idx = (*m_digits)[pos];
  if (idx) {
    idx -= '2';
    if (idx <= 7) {                 // 0 = '2' ... 7 = '9'
      char ch = "adgjmptw"[idx];    // get first letter
      char ch2 = ch + (idx == 5 || idx == 7 ? 4 : 3);  // get last letter + 1
      do {
        m_current[pos] = ch++;      // place letter to local result string
        decipher_impl(pos+1);       // go to next level
      } while(ch < ch2);
    } else {
      m_current[pos] = '?';         // unknown number
      decipher_impl(pos+1);         // go to next level
    }
  } else {
    m_result->push_back(m_current); // add local string to resulting string list if (pos >= m_digits->size())
  }
}

void show_str_list(const vector<string>& list)
{
  cout << '{';
  bool first = true;
  for (const string& s : list) {
    if (!first) { cout << ','; }
    cout << " \"" << s << '"';
    first = false;
  }
  cout << " }" << endl;
}

int main()
{
  vector<string> list;
  PhoneDecipher pd;

  pd.decipher("", list);
  cout << "\"\":\t";
  show_str_list(list);

  pd.decipher("2", list);
  cout << "\"2\":\t";
  show_str_list(list);

  pd.decipher("23", list);
  cout << "\"23\":\t";
  show_str_list(list);

  pd.decipher("712x", list);
  cout << "\"712x\":\t";
  show_str_list(list);

  pd.decipher("8645327", list);
  cout << "\"8645327\":\t";
  cout << "list size = " << list.size() << " elements, ";
  if (std::binary_search(list.begin(), list.end(), "unilecs")) {
    cout << "\"unilecs\" string is found! ;)";
  } else {
    cout << "\"unilecs\" string is NOT found! :(";
  }
  cout << endl;

  pd.decipher("123456789753", list);
  cout << "\"123456789753\":\t";
  cout << "list size = " << list.size() << " elements." << endl;
}