Question

I’m attempting to create a recursive function that outputs a vector of strings that contains all possible word combinations (while retaining order of letters) of a given string. Basically, the foundation of an auto-correct typing program, which produces effects similar that of the iPhone.

vector<string> allPossibleWords(string str, vector<vector<char> > & adjacentKeys)
{
  vector<string> words;

  cout << str << endl;

  if (str.length() == 0)
  {
    return words;
  }

  char firstLetter = str[0];
  string restOf = str.substr(1, str.length() - 1);
  int position = position_in_vector(firstLetter);

  for (int i = 0; i < adjacentKeys[position].size(); i++) 
  {
    string temp(1, adjacentKeys[position][i]);
    words.push_back(temp);
  }

  //allPossibleWords(restOf, adjacentKeys);
}

int position_in_vector(char letter)
{
  return (letter % 97);
}

For instance, if str is “yp”, the output should be a vector containing the values {“yp”, “tp”, “gp”, “hp”, “up”, “yo”, “to”, “go”, “ho”, “uo”, “yl”, “tl”, “gl”, “hl”, “ul”}. If str is “y”, the output should be a vector containing the values {“y”, “t”, “g”, “h”, “u”}.

The 26 vectors stored in adjacentKeys contain the letters adjacent to the letter that is stored in the first position of the vector.

a   qwsz
b   vghjn
c   xdfgv
d   zserfcx
//and so on

I am stuck with this function, and can’t figure out how to recursively build this vector.

Answer 1

(Update: 2130 GMT Sunday: I’ve significantly changed my answer. I think this works now.)

Here is a complete program. There are other changes I think I would make, but I’m trying to keep to the spirit of your initial solution. It’s important to return a single empty word when str.length()==0.

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


vector<string> allPossibleWords(string str, vector<vector<char> > & adjacentKeys)
{
        vector<string> words;

        // cout << "str=" << str << endl;

        if (str.length() == 0)
        {
                words.push_back("");
                return words;
        }

        char firstLetter = str[0];
        // cout << "firstLetter=" << firstLetter << endl;
        int positionInAdjacentKeys = 0;
        while(positionInAdjacentKeys < adjacentKeys.size() && adjacentKeys.at(positionInAdjacentKeys).front() != firstLetter) {
                ++ positionInAdjacentKeys;
        }
        vector<char> & adjacent = adjacentKeys.at(positionInAdjacentKeys);

        string restOf = str.substr(1, str.length() - 1);
        // cout << firstLetter << ":" << restOf << endl;

        // int position = position_in_vector(firstLetter);

        vector<string> recursiveWords = allPossibleWords(restOf, adjacentKeys);

        for (int i = 0; i < adjacent.size(); i++)
        {
                const string temp(1, adjacent[i]);
                // cout << "  temp=" << temp << endl;
                for(vector<string>::const_iterator i = recursiveWords.begin(); i != recursiveWords.end(); i++)
                {
                        // cout << "new word=" <<  temp + *i << endl;
                        words.push_back(temp + *i);
                }
        }
        return  words;
}


int main() {
        vector<vector<char> > adj;
        vector<char> v1;
        v1.clear();
        v1.push_back('p');
        v1.push_back('o');
        v1.push_back('l');
        adj.push_back(v1);
        v1.clear();
        v1.push_back('y');
        v1.push_back('t');
        v1.push_back('g');
        v1.push_back('h');
        v1.push_back('u');
        adj.push_back(v1);
        adj.push_back(v1);

        vector<string> words = allPossibleWords("yp", adj);

        for(vector<string> :: const_iterator i = words.begin(); i != words.end(); i++) {
                cout << *i << endl;
        }
}

return