Run Length Encoding in Python

Given an input string, write a function that returns the Run Length Encoded string for the input string. For example, if the input string is ‘wwwwaaadexxxxxx’, then the function should return ‘w4a3d1e1x6’. 

Examples:

Input  :  str = 'wwwwaaadexxxxxx'
Output : 'w4a3d1e1x6'

This problem has existing solution please refer Run Length Encoding link. Here we will solve this problem quickly in python using OrderedDict. Approach is very simple, first we create a ordered dictionary which contains characters of input string as key and 0 as their default value, now we run a loop to count frequency of each character and will map it to it’s corresponding key. 

Implementation:

Python3

# Python code for run length encoding
from collections import OrderedDict
def runLengthEncoding(input):

    # Generate ordered dictionary of all lower
    # case alphabets, its output will be
    # dict = {'w':0, 'a':0, 'd':0, 'e':0, 'x':0}
    dict=OrderedDict.fromkeys(input, 0)

    # Now iterate through input string to calculate
    # frequency of each character, its output will be
    # dict = {'w':4,'a':3,'d':1,'e':1,'x':6}
    for ch in input:
        dict[ch] += 1

    # now iterate through dictionary to make
    # output string from (key,value) pairs
    output = ''
    for key,value in dict.items():
        output = output + key + str(value)
    return output

# Driver function
if __name__ == "__main__":
    input="wwwwaaadexxxxxx"
    print (runLengthEncoding(input))

Output

w4a3d1e1x6

Another code:

Python3

def encode(message):
    encoded_message = ""
    i = 0

    while (i <= len(message)-1):
        count = 1
        ch = message[i]
        j = i
        while (j < len(message)-1):
            if (message[j] == message[j+1]):
                count = count+1
                j = j+1
            else:
                break
        encoded_message=encoded_message+str(count)+ch
        i = j+1
    return encoded_message

#Provide different values for message and test your program
encoded_message=encode("ABBBBCCCCCCCCAB")
print(encoded_message)

Output

1A4B8C1A1B

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