Related Articles
All combinations of strings that can be used to dial a number
• Difficulty Level : Medium
• Last Updated : 06 Nov, 2020

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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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. Below is Java implementation of this idea.

 `// 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 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 hm =``                    ``new` `HashMap();`` ` `        ``// 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"``);``    ``}``}`

Output :

`AD AE AF BD BE BF CD CE CF `

This article is contributed by Phalgun. 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.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with industry experts, please refer Geeks Classes Live

My Personal Notes arrow_drop_up