Find all strings formed from characters mapped to digits of a number

Consider below list where each digit from 1 to 9 maps to few characters.

1 -> ['A', 'B', 'C']
2 -> ['D', 'E', 'F']
3 -> ['G', 'H', 'I']
4 -> ['J', 'K', 'L']
5 -> ['M', 'N', 'O']
6 -> ['P', 'Q', 'R']
7 -> ['S', 'T', 'U']
8 -> ['V', 'W', 'X']
9 -> ['Y', 'Z']

Given a number, replace its digits with corresponding characters in given list and print all strings possible. Same character should be considered for every occurrence of a digit in the number. Input number is positive and doesn’t contain 0.

Examples :

Input : 121
Output : ADA BDB CDC AEA BEB CEC AFA BFB CFC

Input : 22
Output : DD EE FF

The idea is for each digit in the input number, we consider strings formed by previous digit and append characters mapped to current digit to them. If this is not the first occurrence of the digit, we append same character as used in its first occurrence.

C++

// C++ program to find all strings formed from a given 
// number where each digit maps to given characters. 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to find all strings formed from a given 
// number where each digit maps to given characters. 
vector<string> findCombinations(vector<int> input, 
                                vector<char> table[]) 
{ 
    // vector of strings to store output 
    vector<string> out, temp; 
  
    // stores index of first occurrence 
    // of the digits in input 
    unordered_map<int, int> mp; 
  
    // maintains index of current digit considered 
    int index = 0; 
  
    // for each digit 
    for (int d: input) 
    { 
        // store index of first occurrence 
        // of the digit in the map 
        if (mp.find(d) == mp.end()) 
            mp[d] = index; 
  
        // clear vector contents for future use 
        temp.clear(); 
  
        // do for each character thats maps to the digit 
        for (int i = 0; i < table[d - 1].size(); i++) 
        { 
            // for first digit, simply push all its 
            // mapped characters in the output list 
            if (index == 0) 
            { 
                string s(1, table[d - 1].at(i)); 
                out.push_back(s); 
            } 
  
            // from second digit onwards 
            if (index > 0) 
            { 
                // for each string in output list 
                // append current character to it. 
                for(string str: out) 
                { 
                    // convert current character to string 
                    string s(1, table[d - 1].at(i)); 
  
                    // Imp - If this is not the first occurrence 
                    // of the digit, use same character as used 
                    // in its first occurrence 
                    if(mp[d] != index) 
                        s = str[mp[d]]; 
  
                    str = str + s; 
  
                    // store strings formed by current digit 
                    temp.push_back(str); 
                } 
  
                // nothing more needed to be done if this 
                // is not the first occurrence of the digit 
                if(mp[d] != index) 
                    break; 
            } 
        } 
  
        // replace contents of output list with temp list 
        if(index > 0) 
            out = temp; 
        index++; 
    } 
  
    return out; 
} 
  
// Driver program 
int main() 
{ 
    // vector to store the mappings 
    vector<char> table[] = 
    { 
        { 'A', 'B', 'C' }, 
        { 'D', 'E', 'F' }, 
        { 'G', 'H', 'I' }, 
        { 'J', 'K', 'L' }, 
        { 'M', 'N', 'O' }, 
        { 'P', 'Q', 'R' }, 
        { 'S', 'T', 'U' }, 
        { 'V', 'W', 'X' }, 
        { 'Y', 'Z' } 
    }; 
  
    // vector to store input number 
    vector<int> input = { 1, 2, 1}; 
  
    vector<string> out = findCombinations(input, table); 
  
    // print all possible strings 
    for (string it: out) 
        cout << it << " "; 
  
    return 0; 
} 

Python3

# Python program to find all strings formed from a given 
# number where each digit maps to given characters. 
  
# Function to find all strings formed from a given 
# number where each digit maps to given characters. 
def findCombinations(input: list, table: list) -> list: 
  
    # vector of strings to store output 
    out, temp = [], [] 
  
    # stores index of first occurrence 
    # of the digits in input 
    mp = dict() 
  
    # maintains index of current digit considered 
    index = 0
  
    # for each digit 
    for d in input: 
  
        # store index of first occurrence 
        # of the digit in the map 
        if d not in mp: 
            mp[d] = index 
  
        # clear vector contents for future use 
        temp.clear() 
  
        # do for each character thats maps to the digit 
        for i in range(len(table[d - 1])): 
  
            # for first digit, simply push all its 
            # mapped characters in the output list 
            if index == 0: 
                s = table[d - 1][i] 
                out.append(s) 
  
            # from second digit onwards 
            if index > 0: 
  
                # for each string in output list 
                # append current character to it. 
                for string in out: 
  
                    # convert current character to string 
                    s = table[d - 1][i] 
  
                    # Imp - If this is not the first occurrence 
                    # of the digit, use same character as used 
                    # in its first occurrence 
                    if mp[d] != index: 
                        s = string[mp[d]] 
  
                    string = string + s 
  
                    # store strings formed by current digit 
                    temp.append(string) 
  
                # nothing more needed to be done if this 
                # is not the first occurrence of the digit 
                if mp[d] != index: 
                    break
  
        # replace contents of output list with temp list 
        if index > 0: 
            out = temp.copy() 
        index += 1
    return out 
  
# Driver Code 
if __name__ == "__main__": 
  
    # vector to store the mappings 
    table = [['A', 'B', 'C'], 
            ['D', 'E', 'F'], 
            ['G', 'H', 'I'], 
            ['J', 'K', 'L'], 
            ['M', 'N', 'O'], 
            ['P', 'Q', 'R'], 
            ['S', 'T', 'U'], 
            ['V', 'W', 'X'], 
            ['Y', 'Z']] 
  
    # vector to store input number 
    input = [1, 2, 1] 
    out = findCombinations(input, table) 
  
    # print all possible strings 
    for it in out: 
        print(it, end=" ") 
  
# This code is contributed by 
# sanjeev2552 

Output :

ADA BDB CDC AEA BEB CEC AFA BFB CFC

This article is contributed by Aditya Goel. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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My Personal Notes

C++

Python3

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