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Letter Combinations of a Phone Number

Explore how to generate all letter combinations corresponding to digits on a phone keypad. Understand the mapping of digits 2 through 9 to letters and practice implementing solutions that handle multiple digit inputs up to length four.

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Statement

Given a string containing digits from 2 to 9 inclusive, with the possibility of each digit appearing multiple times, return all possible letter combinations that the number could represent. Return the answer in any order.

The illustration below shows the mapping of digits to letters in a telephone dial pad.

Note: The number 11 on the telephone dial pad does not correspond to any letter, so the input string only contains digits from 22 to 99.

Constraints:

  • 0≤0 \leq digits.length ≤4\leq 4

  • digits[i] is a digit in the range [2,9][2, 9]

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Letter Combinations of a Phone Number

1.

What should be the output if the following digits are given as input?

Digits = 29

A.

[aw, ax, ay, az]

B.

[bw, bx, by, bz]

C.

[aw, ax, ay, az, bw, bx, by, bz, cw, cx, cy, cz]

D.

[cw, cx, cy, cz]

1 / 4

Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4
5

Try it yourself

Implement your solution in the following coding playground:

Java
usercode > Main.java
import java.util.*;



public class Main{

    public List<String> letterCombinations(String digits){



        // Replace this placeholder return statement with your code



        return new ArrayList<>();

    }

}
Letter Combinations of a Phone Number