Summary

Started in 2008 and recently resurging in popularity, a game known as Number Neighbour or Text Door Neighbor has people sending a text message to phone numbers near their own. Traditionally this was done for numbers ±1, so someone with the phone number 555-555-5555 has neighbors 555-555-5554 and 555-555-5556.

We're going to take this a step further and think about neighbors based on a classic phone keypad.

First, let's take a look at the classic phone keypad:

1 2 3
4 5 6
7 8 9
  0

We can consider certain numbers adjacent if they appear directly next to or above/below each other. For example, 1 is adjacent to 2 and 4 (and nothing else), while 5 is adjacent to 2, 4, 6, and 8.

Let's look for phone numbers that are "neighbors" of a given phone number by having any one (and only one) of their digits be off-by-one as a number adjacent to the original.

By this definition, 555-555-5555 has both its original neighbors but also, e.g., 554-555-5555 and 555-555-5558.

Problem

Given a phone number of integer length N (1 ≤ N ≤ 10) as a number string (e.g. 555-555-5555 would be passed as "5555555555"), return an array of all phone numbers as number strings that would be considered neighbors of that phone number.

Examples

Given:

  "1"

Return:

  ["2", "4"]

Given:

  "8675309"

Return:

  ["5675309", "7675309", "9675309", "0675309", "8375309", "8575309", "8975309",
   "8645309", "8685309", "8672309", "8674309", "8676309", "8678309", "8675209",
   "8675609", "8675389", "8675306", "8675308"]

Notes

• Do not wrap around a side of the keypad when finding adjacent numbers. That is, do not consider 6 adjacent to 4 nor 0 adjacent to 2.
• Do not consider numbers that are diagonal to each other adjacent
• Do not worry about invalid characters, nil, or anything other than a valid number string being passed in
• Do not worry about the order of number strings in the array being returned