Problem Statement

Given a string digits containing digits from 2-9, return an array of strings containing all possible letter combinations that the number could represent. You may return the answer in any order.

The mapping of digits to letters (just like on the telephone buttons) is as given below.

• 1 -> It doesn't map any number.
• 2 -> "abc"
• 3 -> "def"
• 4 -> "ghi"
• 5 -> "jkl"
• 6 -> "mno"
• 7 -> "pqrs"
• 8 -> "tuv"
• 9 -> "wxyz"

Examples

• Example 1:

  • Input: digits = "47"
  • Expected Output: ["gp", "gq", "gr", "gs", "hp", "hq", "hr", "hs", "ip", "iq", "ir", "is"]
  • Justification: The digit '4' maps to "ghi", and '7' maps to "pqrs". Combining these letters in every possible way gives us the expected output.

• Example 2:

  • Input: digits = "29"
  • Expected Output: ["aw", "ax", "ay", "az", "bw", "bx", "by", "bz", "cw", "cx", "cy", "cz"]
  • Justification: The digit '2' maps to "abc", and '9' maps to "wxyz". The combinations of these letters result in the expected output.

• Example 3:

  • Input: digits = "7"
  • Expected Output: ["p", "q", "r", "s"]
  • Justification: The digit '7' maps to "pqrs". All possible combinations of these letters are reflected in the expected output.

Constraints:

• 0 <= digits.length <= 4
• digits[i] is a digit in the range ['2', '9'].

Try it yourself

Try solving this question here: