Question

PLEASE CODE IN PYTHON

Run-length encoding is a simple compression scheme best used when a data-set consists primarily of numerous, long runs of repeated characters. For example, AAAAAAAAAA is a run of 10 A’s. We could encode this run using a notation like *A10, where the * is a special flag character that indicates a run, A is the symbol in the run, and 10 is the length of the run. As another example, the string

KKKKKKKKKKKKKBCCDDDDDDDDDDDDDDDKKKKKMNUUUGGGGG

would be encoded

$K13BCC$D15$K5MNUUU$G5

assuming in this case that $ is the flag character. For the sake of this problem we will assume that the input strings to be encoded contain only uppercase letters from the Latin alphabet and that no run is longer than 99 characters long. Flag characters will be chosen only from the set {#, $, &, *}. Note that single letters (’M’), runs of two letters (’CC’), and runs of three letters (’UUU’) are not encoded, as doing so does not save memory or actually compress the data. Do you see why that is the case?

Write the function def rle(string, flag) that takes a non-empty string to encode and a character to use as the flag character. The function returns the run-length encoded argument string. If the string to encode contains any characters except uppercase letters, the function should return the string ’ERROR’ (without the quotation marks). If the flag character is not one of the symbols in the set {#, $, &, *}, the function should return the string ’ERROR’. Consider using a while-loop instead of a for-loop to iterate over the string. Start with an empty string (which will eventually contain the returned result) and keep a counter for the number of identical characters you find in each run. When a run ends, append (i) the flag character, (ii) the count, and (iii) the character itself to the result. Remember that only runs of length 4 or greater should be encoded; single characters, pairs and triples should simply be appended to the result.

Answer 1

"""

Author:ravi
Date :5/4/17
File Name:run_length_encoding.py
Description:

"""


def rle(string, flag):
    """

    :param string:
    :param flag:
    :return:
    """
    count = 0  # store the count of repeated character
    prev = string[0]  # store previous character
    result = ''  # store resultant string
    index = 0  # store the next index to process
    while index < len(string):  # iterate the string using while loop
        # if string has  lower case character  or other than alphabet or flag has
        # character other than #$&*
        if not string[index].isalpha() or string[index].islower() or flag not in '#$&*':
            return "ERROR"  # return ERROR
        if prev == string[index]:
            count += 1

        else:
            if count > 3:
                result += flag + prev + str(count)

            else:
                result += prev * count
            count = 1

        prev = string[index]
        index += 1
        if index == len(string):  # check index is equal to string length
            if count > 3:
                result += flag + prev + str(count)

            else:
                result += prev * count

    return result


if __name__ == '__main__':
    print("\n" + rle("GGGGG", "#"))
    print("\n" + rle("XYZAAAAAAGGTCCCCCCTTTAAAAAAAAAAAAAAKK", "*"))
    print("\n" + rle("ABCCDEFGGG", "$"))
    print("\n" + rle("ABCCDEFGGGG", "$"))
    print("\n" + rle("XYZAAAAAAGGTCCCCCCTTTaAAAAAAAAAAAAAKK", "*"))
    print("\n" + rle("XYZAAAAAAGGTCCCCCCTTTAAAAAAAAAAAAAAKK", "!"))

output:

#G5 XYZ*A6GGT C6TTT*A14KK ABCCDEFGGG ABCCDEF$G4 ERROR ERROR Process finished with exit code 0