How to resolve the algorithm UPC step by step in the Ruby programming language

Published on 12 May 2024 09:40 PM
#Ruby

How to resolve the algorithm UPC step by step in the Ruby programming language

Table of Contents

Problem Statement

Convert UPC bar codes to decimal.

Specifically: The UPC standard is actually a collection of standards -- physical standards, data format standards, product reference standards... Here,   in this task,   we will focus on some of the data format standards,   with an imaginary physical+electrical implementation which converts physical UPC bar codes to ASCII   (with spaces and   #   characters representing the presence or absence of ink).

Below, we have a representation of ten different UPC-A bar codes read by our imaginary bar code reader: Some of these were entered upside down,   and one entry has a timing error.

Implement code to find the corresponding decimal representation of each, rejecting the error. Extra credit for handling the rows entered upside down   (the other option is to reject them).

Each digit is represented by 7 bits: On the left hand side of the bar code a space represents a 0 and a # represents a 1. On the right hand side of the bar code, a # represents a 0 and a space represents a 1 Alternatively (for the above):   spaces always represent zeros and # characters always represent ones, but the representation is logically negated -- 1s and 0s are flipped -- on the right hand side of the bar code.

Finally, the last digit is a checksum digit which may be used to help detect errors.

Multiply each digit in the represented 12 digit sequence by the corresponding number in   (3,1,3,1,3,1,3,1,3,1,3,1)   and add the products. The sum (mod 10) must be 0   (must have a zero as its last digit)   if the UPC number has been read correctly.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm UPC step by step in the Ruby programming language

The provided Ruby code is designed to decode Universal Product Codes (UPCs) and determine their validity. A UPC is a 12-digit numeric code that uniquely identifies a product and is commonly printed on product packaging. The code consists of two parts: a 6-digit left-hand side and a 6-digit right-hand side, separated by a middle sentinel character (" # # "). Additionally, the code is enclosed within two end sentinel characters ("# #").

The code is organized as follows:

  1. DIGIT_F and DIGIT_R constants: These constants define mappings between strings representing the shape of individual digits and their corresponding numeric values. DIGIT_F maps digit shapes for the left-hand side, while DIGIT_R maps digit shapes for the right-hand side.

  2. END_SENTINEL and MID_SENTINEL constants: These constants define the strings that represent the end sentinel and middle sentinel characters, respectively.

  3. decode_upc_impl method: This method is responsible for the core decoding logic. It takes an input string, which represents the UPC, and attempts to decode it. The method performs the following steps: a. It checks if the input string is 95 characters long, since a valid UPC should consist of 95 characters. b. It checks for the presence of end sentinel characters at the beginning and end of the string. c. It iterates through the string to extract the 6 left-hand side digits and calculates their sum using the appropriate weightings (1 or 3). d. It checks for the presence of the middle sentinel character. e. It iterates through the string to extract the 6 right-hand side digits and calculates their sum using the appropriate weightings. f. It checks for the presence of end sentinel characters at the end of the string. g. It verifies if the sum of the digits is divisible by 10, which is a checksum validation for UPCs. h. If all checks pass, it prints the decoded digits and returns True to indicate a successful decode. Otherwise, it prints an error message and returns False.

  4. decode_upc method: This method serves as a wrapper for the decode_upc_impl method. It takes an input string and attempts to decode it. If the decode is successful for either the original string or its reverse, it prints the appropriate message indicating whether the code was read right-side up or upside down. If the decode fails for both orientations, it prints an error message.

  5. main method: This method serves as the entry point for the program. It defines 10 sample UPCs and calls decode_upc for each sample, printing the results.

Here's a breakdown of the execution flow:

  1. The program reads the sample UPCs defined in the main method.
  2. For each sample UPC, it calls the decode_upc method, which in turn calls the decode_upc_impl method for both the original string and its reverse.
  3. The decode_upc_impl method validates the format of the UPC, calculates the sum of the digits, and checks the checksum.
  4. If the checksum is valid, the method prints the decoded digits and returns True. Otherwise, it returns False.
  5. The decode_upc method prints an appropriate message based on the results of decode_upc_impl for both orientations of the input string.

By executing these steps, the code attempts to decode each sample UPC and determine its validity. If the code is valid, it indicates whether it was read right-side up or upside down. If the code is invalid, it prints an error message.

Source code in the ruby programming language

DIGIT_F = {
    "   ## #" => 0,
    "  ##  #" => 1,
    "  #  ##" => 2,
    " #### #" => 3,
    " #   ##" => 4,
    " ##   #" => 5,
    " # ####" => 6,
    " ### ##" => 7,
    " ## ###" => 8,
    "   # ##" => 9,
}

DIGIT_R = {
    "###  # " => 0,
    "##  ## " => 1,
    "## ##  " => 2,
    "#    # " => 3,
    "# ###  " => 4,
    "#  ### " => 5,
    "# #    " => 6,
    "#   #  " => 7,
    "#  #   " => 8,
    "### #  " => 9,
}

END_SENTINEL = "# #"
MID_SENTINEL = " # # "

def decode_upc(s)
    def decode_upc_impl(input)
        upc = input.strip
        if upc.length != 95 then
            return false
        end

        pos = 0
        digits = []
        sum = 0

        # end sentinel
        if upc[pos .. pos + 2] == END_SENTINEL then
            pos += 3
        else
            return false
        end

        # 6 left hand digits
        for i in 0 .. 5
            digit = DIGIT_F[upc[pos .. pos + 6]]
            if digit == nil then
                return false
            else
                digits.push(digit)
                sum += digit * [1, 3][digits.length % 2]
                pos += 7
            end
        end

        # mid sentinel
        if upc[pos .. pos + 4] == MID_SENTINEL then
            pos += 5
        else
            return false
        end

        # 6 right hand digits
        for i in 0 .. 5
            digit = DIGIT_R[upc[pos .. pos + 6]]
            if digit == nil then
                return false
            else
                digits.push(digit)
                sum += digit * [1, 3][digits.length % 2]
                pos += 7
            end
        end

        # end sentinel
        if upc[pos .. pos + 2] == END_SENTINEL then
            pos += 3
        else
            return false
        end

        if sum % 10  == 0 then
            print digits, " "
            return true
        else
            print "Failed Checksum "
            return false
        end
    end

    if decode_upc_impl(s) then
        puts "Rightside Up"
    elsif decode_upc_impl(s.reverse) then
        puts "Upside Down"
    else
        puts "Invalid digit(s)"
    end
end

def main
    num = 0

    print "%2d: " % [num += 1]
    decode_upc("         # #   # ##  #  ## #   ## ### ## ### ## #### # # # ## ##  #   #  ##  ## ###  # ##  ## ### #  # #       ")

    print "%2d: " % [num += 1]
    decode_upc("        # # #   ##   ## # #### #   # ## #   ## #   ## # # # ###  # ###  ##  ## ###  # #  ### ###  # # #         ")

    print "%2d: " % [num += 1]
    decode_upc("         # #    # # #  ###  #   #    # #  #   #    # # # # ## #   ## #   ## #   ##   # # #### ### ## # #         ")

    print "%2d: " % [num += 1]
    decode_upc("       # # ##  ## ##  ##   #  #   #  # ###  # ##  ## # # #   ## ##  #  ### ## ## #   # #### ## #   # #        ")

    print "%2d: " % [num += 1]
    decode_upc("         # # ### ## #   ## ## ###  ##  # ##   #   # ## # # ### #  ## ##  #    # ### #  ## ##  #      # #          ")

    print "%2d: " % [num += 1]
    decode_upc("          # #  #   # ##  ##  #   #   #  # ##  ##  #   # # # # #### #  ##  # #### #### # #  ##  # #### # #         ")

    print "%2d: " % [num += 1]
    decode_upc("         # #  #  ##  ##  # #   ## ##   # ### ## ##   # # # #  #   #   #  #  ### # #    ###  # #  #   # #        ")

    print "%2d: " % [num += 1]
    decode_upc("        # # #    # ##  ##   #  # ##  ##  ### #   #  # # # ### ## ## ### ## ### ### ## #  ##  ### ## # #         ")

    print "%2d: " % [num += 1]
    decode_upc("         # # ### ##   ## # # #### #   ## # #### # #### # # #   #  # ###  #    # ###  # #    # ###  # # #       ")

    print "%2d: " % [num += 1]
    decode_upc("        # # # #### ##   # #### # #   ## ## ### #### # # # #  ### # ###  ###  # # ###  #    # #  ### # #         ")
end

main()

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