String encoding & decoding

Description

• Given an encoded string and the number of rows of the matrix used for encoding, return the decoded string.

• Example:

• input: "mnes__ya___mi"
• output: "my name is"
• Encoding matrix

[
  ["m", "n", "e", "s", " "],
  [" ", "y", "a", " ", " "],
  [" ", " ", " ", "m", "i"]
]

Solution steps

• Decoding

• First of all, check if the input parameters were passed (encodedStr and numOfRows). Also check if the number of rows is greater than zero.

• Determine the number of columns for the matrix.
• Populate the matrix sequentially with the letters of encodedStr.
• Once the matrix is populate, read the letters from the matrix in the correct order and join the letters.

• Trim the decoded string (remove trailing spaces, for example) and return the decoded result.

• Encoding

• Check if the input parameters were passed (str and numOfRows). Also checks if the number of rows is greater than zero.

• Determine the number of rows for the matrix.
• Initialize the matrix with empty values with the dimension numOfRows*numOfColumns.
• Populate the matrix with the letters of the plain string in the correct order.
• Join the elements of the matrix in sequential order.
• Return the encoded string.

Runtime complexity

• The runtime complexity for the decodeString method is based on the dimension of the encoding matrix.
• The dimension of the matrix can be calculated with the function d = r*(n/r), where:
• n is the length of the encodedStr input.
• r is the integer numOfRows input.
• Simplifying the function d = r*(n/r) we get d = n.
• Therefore the runtime complexity is: O(n).

Tests

# install jest dependency
npm i

# run tests
npm run test