pyLongestAscendingSubstring

# A function to find the longest substring of ascending value characters


def longest_ascending_substring(s1):
    last_char = chr(255)            # Initialise last_char to the highest ASCII value (simplifies later process)
    s1 += chr(0)                    # Append the lowest ASCII value to our input string (simplifies processing)
    substring = ""                  # Initialise an empty variable for substring
    longest_substring = ""          # Initialise a variable that will hold the longest substring encountered

    for ch in s1:                   # Examine one character at a time from the input string
        if ch < last_char:                          # end of an ascending sequence
            # An ascending sequence has ended. Was it the longest such sequence found so far?
            if len(substring) > len(longest_substring):
                longest_substring = substring       # remember the longest substring so far
            substring = ""          # start a new empty substring
        substring += ch             # add current character to current sub-string
        last_char = ch              # remember the last character for sequence checking
    return(longest_substring)


tests = ["abcbad", "abcbcde", "gkcmqqfebrtvxp", "jollyhockeystick"]
for test in tests:
    print(test, " >> ", longest_ascending_substring(test))

# Results:-
#
# abcbad  >>  abc
# abcbcde  >>  bcde
# gkcmqqfebrtvxp  >>  brtvx
# jollyhockeystick  >>  lly