The challenge
Find the longest substring in alphabetical order.
Example:
the longest alphabetical substring in "asdfaaaabbbbcttavvfffffdf"
is "aaaabbbbctt"
.
Overview:
There are tests with strings up to 10 000
characters long so your code will need to be efficient.
The input will only consist of lowercase characters and will be at least one letter long.
If there are multiple solutions, return the one that appears first.
The solution in Python
Option 1:
import re
reg = re.compile('a*b*c*d*e*f*g*h*i*j*k*l*m*n*o*p*q*r*s*t*u*v*w*x*y*z*')
def longest(s):
return max(reg.findall(s), key=len)
Code language: Python (python)
Option 2:
def longest(s):
k = []
for i in range(len(s)-1):
if s[i] <= s[i+1]:
k.append(s[i])
else:
k.append(s[i])
k.append(' ')
k += s[-1]
return max(''.join(k).split(), key=len)
Code language: Python (python)
Option 3:
def longest(s):
chunks = []
for c in s:
if chunks and chunks[-1][-1] <= c:
chunks[-1] += c
else:
chunks.append(c)
return max(chunks, key=len)
Code language: Python (python)
Test cases to validate our solution
test.assert_equals(longest('asd'), 'as')
test.assert_equals(longest('nab'), 'ab')
test.assert_equals(longest('abcdeapbcdef'), 'abcde')
test.assert_equals(longest('asdfaaaabbbbcttavvfffffdf'), 'aaaabbbbctt')
test.assert_equals(longest('asdfbyfgiklag'), 'fgikl')
test.assert_equals(longest('z'), 'z')
test.assert_equals(longest('zyba'), 'z')
Code language: Python (python)