def reverse_words(sentence):
# Handle some error cases
if len(sentence) == 0:
return sentence
reversed = []
last_idx = len(sentence) - 1
lead = last_idx
trail = last_idx
# Only do this until we are at the end of the array
# we will be filling. When trail falls below 0,
# then we should stop iterating.
while len(reversed) < len(sentence) and trail > 0:
# We need two pointers: 1) to find the leading
# edge of a word, and one to find the trailing
# edge of a word, and then we can slice the
# string and put it in the right spot.
while sentence[lead] == ' ' and lead >= 0:
#print(lead)
lead -= 1
# We have found the start of the first word.
# Now we need to find the end.
trail = lead
while sentence[trail] != ' ' and trail >= 0:
#print(trail)
trail -= 1
# Now the trail points to one past the end of the last
# word, which could be off the end of the array.
# Now, we want to use this slice to get the first word
# Add 1 to the pointers so we don't iterate below a 0
# index.
# If we already have a word in here, then add a space between.
if len(reversed) > 0:
reversed.append(' ')
reversed.extend(sentence[(trail+1):(lead+1)])
# We want to update our other pointer to be at this same
# spot, so it will continue to iterate on the next loop
# and find the beginning of the next word.
lead = trail
return ''.join(reversed)
Course: Grokking Coding Interview Patterns in Python - Learn Interactively
Lesson: Solution: Reverse Words in a String - Grokking Coding Interview Patterns in Python
