All combinations of strings that can be used to dial a number

Last Updated : 13 Aug, 2024

Given a number, print all possible combinations of strings that can be used to dial the given number in a phone with following specifications. In the given phone, we can dial, 2 using A or B or C, 3 using D or E or F, ................... 8 using T or U or V, 9 using W or X or Y or Z, 1 using only 1 0 using 0. For example if 23, is the given phone number, the program should print AD, AE, AF, BD, BE, BF, CD, CE, CF

The idea is to store digit to characters mapping in hash map. The map stores all characters that can be used dial a digit. We place every possible character for current digit and recur for remaining digits.

Algorithm:

Create a hash map with keys as digits from 0 to 9 and values as the set of characters associated with each digit.
Define a recursive function printStrings that takes four arguments:
a. phNo - the input phone number
b. i - the index of the current digit being processed
c. hm - the hash map of digit to character sets
d. str - the string of characters generated so far
Inside the printStrings function:
a. Check if i has reached the end of the phone number. If yes, print the generated string and return.
b. Get the set of characters associated with the current digit from the hash map.
c. Iterate over each character in the set and:
i. Append the character to the string str.
ii. Recursively call the printStrings function for the next digit.
iii. Remove the last character from the string str.
Define a function printStringForNumber that takes one argument:
a. phNo - the input phone number
Inside the printStringForNumber function, call the printStrings function with the arguments phNo, 0, hm, and an empty string.

Below is Java implementation of this idea.

Implementation:

C++

// C++ program for the above approach

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

void printStrings(string phNo, int i,
                unordered_map<char, string> hm,
                string str)
{
    if (i == phNo.length())
    {
        cout << str << " ";
        return;
    }

    string s = hm[phNo[i]];
    for (int j = 0; j < s.length(); j++)
    {
        str.push_back(s[j]);
        printStrings(phNo, i+1, hm, str);
        str.pop_back();
    }
}

void printStringForNumber(string phNo)
{
    unordered_map<char, string> hm = {
                    {'2', "ABC"},
                    {'3', "DEF"},
                    {'4', "GHI"},
                    {'5', "JKL"},
                    {'6', "MNO"},
                    {'7', "PQRS"},
                    {'8', "TUV"},
                    {'9', "WXYZ"},
                    {'1', "1"},
                    {'0', "0"}
    };

    string str;
    printStrings(phNo, 0, hm, str);
}

int main()
{
    printStringForNumber("23");
    return 0;
}

// This code is contributed by codebraxnzt

Java

// Java program to print all possible key strings
// that can be used to dial a phone number.
import java.util.HashMap;

class ConvertToString
{
    // A Recursive function to print all combinations
    // that can be used to dial a given number.
    // phNo ==> Given Phone Number
    // i ==> Current digit of phNo to be processed
    // hm ==> Stores characters that can be used to
    //         to dial a digit.
    // str ==> Current output string
    static void printStrings(String phNo, int i,
                    HashMap<Character, String> hm,
                    StringBuilder str)
    {
        // If all digits are processed, print output
        // string
        if (i == phNo.length())
        {
            System.out.print(str + " ");
            return;
        }

        // Get current digit of phNo, and recur for all
        // characters that can be used to dial it.
        String s = hm.get(phNo.charAt(i));
        for (int j = 0; j < s.length(); j++)
        {
            str.append(s.charAt(j));
            printStrings(phNo, i+1, hm, str);
            str.deleteCharAt(str.length()-1);
        }
    }

    // Prints all possible combinations of strings that
    // can be used to dial c[].
    static void printStringForNumber(String phNo)
    {
        // Create a HashMap
        HashMap<Character, String> hm =
                    new HashMap<Character, String>();

        // For every digit, store characters that can
        // be used to dial it.
        hm.put('2', "ABC");
        hm.put('3', "DEF");
        hm.put('4', "GHI");
        hm.put('5', "JKL");
        hm.put('6', "MNO");
        hm.put('7', "PQRS");
        hm.put('8', "TUV");
        hm.put('9', "WXYZ");
        hm.put('1', "1");
        hm.put('0', "0");

        // Create a string to store a particular output
        // string
        StringBuilder str = new StringBuilder();

        // Call recursive function
        printStrings(phNo, 0, hm, str);
    }

    // Driver code to test above methods
    public static void main(String args[])
    {
        // Prints
        printStringForNumber("23");
    }
}

Python

def print_strings(ph_no, i, hm, s):
    if i == len(ph_no):
        print(s, end=" ")
        return
    for c in hm[ph_no[i]]:
        print_strings(ph_no, i+1, hm, s+c)

def print_string_for_number(ph_no):
    hm = {
        '2': "ABC",
        '3': "DEF",
        '4': "GHI",
        '5': "JKL",
        '6': "MNO",
        '7': "PQRS",
        '8': "TUV",
        '9': "WXYZ",
        '1': "1",
        '0': "0"
    }
    s = ""
    print_strings(ph_no, 0, hm, s)

print_string_for_number("23")

using System;
using System.Collections.Generic;

class Program {
    static void printStrings(string phNo, int i,
                             Dictionary<char, string> hm,
                             string str)
    {
        if (i == phNo.Length)
        {
            Console.Write(str + " ");
            return;
        }

        string s = hm[phNo[i]];
        for (int j = 0; j < s.Length; j++)
        {
            str += s[j];
            printStrings(phNo, i+1, hm, str);
            str = str.Remove(str.Length-1);
        }
    }

    static void printStringForNumber(string phNo)
    {
        Dictionary<char, string> hm = new Dictionary<char, string>
        {
            {'2', "ABC"},
            {'3', "DEF"},
            {'4', "GHI"},
            {'5', "JKL"},
            {'6', "MNO"},
            {'7', "PQRS"},
            {'8', "TUV"},
            {'9', "WXYZ"},
            {'1', "1"},
            {'0', "0"}
        };

        string str = "";
        printStrings(phNo, 0, hm, str);
    }

    static void Main(string[] args) {
        printStringForNumber("23");
    }
}

JavaScript

function printStrings(phNo, i, hm, s) {
    if (i === phNo.length) {
        console.log(s + " ");
        return;
    }
    for (let j = 0; j < hm[phNo[i]].length; j++) {
        s += hm[phNo[i]][j];
        printStrings(phNo, i+1, hm, s);
        s = s.slice(0, -1);
    }
}

function printStringForNumber(phNo) {
    let hm = {
        '2': "ABC",
        '3': "DEF",
        '4': "GHI",
        '5': "JKL",
        '6': "MNO",
        '7': "PQRS",
        '8': "TUV",
        '9': "WXYZ",
        '1': "1",
        '0': "0"
    };
    let s = "";
    printStrings(phNo, 0, hm, s);
}

printStringForNumber("23");