Z_Algorithm.py

# Z ALgorithm Function
def Z__Algo(text, pattern):
    List = []
    substring = ""

    """ Iterating upto the index where the substring can occur """
    for text_index in range(0, len(text) - len(pattern)+1):

        """ Extracting the --substring of the same length as pattern-- from the text """
        substring = text[text_index:text_index + len(pattern)]

        """ Loop for comparing the substring and pattern """
        count = 0
        for substring_index in range(0, len(pattern)):

            """ If the charecters of substring and pattern matches , increment count by 1 """
            if substring[substring_index] == pattern[substring_index]:
                count += 1

        """ If all the charecters of substring and pattern matches , add position to list """
        if count == len(pattern):
            List.append(text_index)

    """ Return the list that contains all the positions the substring is present at """
    return List


# Searching Process Driver Code

if __name__ == '__main__':
    text = input("Enter Text : ")
    pattern = input("Enter pattern : ")
    
    """Calling Z__Algo to seacrh the substring positions"""
    positions = Z__Algo(text, pattern)

    """If returned list from Z__Algo is not empty , print positions , else prompt -- pattern not found"""
    if len(positions) != 0:
        for position in positions:
            print("The pattern is present at : " + str(position))

    else:
        print("Pattern Not Found !!!")

        
        
        
        
        
"""
    Input description: 
    Line 1 -- Text
    Line 2 -- Pattern
    
    Output Description :
    The pattern is present at : position_index
    ...
    ...
    
    
    Input 1:        
        aaaabbabbababaabbabaaaa
        aa
    Ouput 1:
        The pattern is present at : 0
        The pattern is present at : 1
        The pattern is present at : 2
        The pattern is present at : 13
        The pattern is present at : 19
        The pattern is present at : 20
        The pattern is present at : 21


    Input 2:
        bbbabbabbaccdcbshdddhh
        bb
    Output 2:
        The pattern is present at : 0
        The pattern is present at : 1
        The pattern is present at : 4
        The pattern is present at : 7

"""