First time programming ever... I'm trying to do this exercise to.. :
Write a program that prints the longest substring of s in which the letters occur in alphabetical order. For example, if s = 'azcbobobegghakl', then your program should print
Longest substring in alphabetical order is: beggh
I was here..before starting to freak out:
s = 'abcdezcbobobegghakl'
n = len(s)
x = 0
x += 1
lengh = s[x-1]
if s[x] >= s[x-1]:
lengh = lengh + s[x]
if s[x+1] < s[x]:
n = len(lengh)
if x > n:
break
print('Longest substring in alphabetical order is: ' + str(lengh))
I know this code is bad..I m trying to find substring in alphabetical order and is some way keep the longest one! I know could be normal, because I never programmed before but i feel really frustrated...any good idea/help??
First try to decompose your problem into little problems (do not optimize ! until your problem is solved), if you have learned about functions they are a good way to decompose execution flow into readable and understandable snippets.
An example to start would be :
def get_sequence_size(my_string, start):
# Your code here
return size_of_sequence
current_position = 0
while current_position < len(my_string):
# Your code here using get_sequence_size() function
The following code solves the problem using the reduce method:
solution = ''
def check(substr, char):
global solution
last_char = substr[-1]
substr = (substr + char) if char >= last_char else char
if len(substr) > len(solution):
solution = substr
return substr
def get_largest(s):
global solution
solution = ''
reduce(check, list(s))
return solution
def find_longest_substr(my_str):
# string var to hold the result
res = ""
# candidate for the longest sub-string
candidate = ""
# for each char in string
for char in my_str:
# if candidate is empty, just add the first char to it
if not candidate:
candidate += char
# if last char in candidate is "lower" than equal to current char, add char to candidate
elif candidate[-1] <= char:
candidate += char
# if candidate is longer than result, we found new longest sub-string
elif len(candidate) > len(res):
res= candidate
candidate = char
# reset candidate and add current char to it
else:
candidate = char
# last candidate is the longest, update result
if len(candidate) > len(res):
res= candidate
return res
def main():
str1 = "azcbobobegghaklbeggh"
longest = find_longest_substr(str1)
print longest
if __name__ == "__main__":
main()
These are all assuming you have a string (s) and are needing to find the longest substring in alphabetical order.
Option A
test = s[0] # seed with first letter in string s
best = '' # empty var for keeping track of longest sequence
for n in range(1, len(s)): # have s[0] so compare to s[1]
if len(test) > len(best):
best = test
if s[n] >= s[n-1]:
test = test + s[n] # add s[1] to s[0] if greater or equal
else: # if not, do one of these options
test = s[n]
print "Longest substring in alphabetical order is:", best
Option B
maxSub, currentSub, previousChar = '', '', ''
for char in s:
if char >= previousChar:
currentSub = currentSub + char
if len(currentSub) > len(maxSub):
maxSub = currentSub
else: currentSub = char
previousChar = char
print maxSub
Option C
matches = []
current = [s[0]]
for index, character in enumerate(s[1:]):
if character >= s[index]: current.append(character)
else:
matches.append(current)
current = [character]
print "".join(max(matches, key=len))
Option D
def longest_ascending(s):
matches = []
current = [s[0]]
for index, character in enumerate(s[1:]):
if character >= s[index]:
current.append(character)
else:
matches.append(current)
current = [character]
matches.append(current)
return "".join(max(matches, key=len))
print(longest_ascending(s))
def longest(s):
buff = ''
longest = ''
s += chr(255)
for i in range(len(s)-1):
buff += s[i]
if not s[i] < s[i+1]:
if len(buff) > len(longest):
longest = buff
buff = ''
if len(buff) > len(longest):
longest = buff
return longest
