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

• Difficulty Level : Hard
• Last Updated : 24 Jan, 2020

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 using namespace std;  // Function to find all strings formed from a given// number where each digit maps to given characters.vector findCombinations(vector input,                                vector table[]){    // vector of strings to store output    vector out, temp;      // stores index of first occurrence    // of the digits in input    unordered_map 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 programint main(){    // vector to store the mappings    vector 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 input = { 1, 2, 1};      vector 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 Codeif __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