CyberStars

Reverse a String

Reversing a string sounds simple (and it is), but it's a classic exercise because it forces you to think about indexing, loops, and building up a result

We already saw one way using the accumulator pattern

original = "Tommy"
reversed_str = ""
for char in original:
    reversed_str = char + reversed_str
print(reversed_str)

Output ymmoT

But Python actually has an even simpler way: slicing

name = "Tommy"
print(name[::-1])

Output ymmoT

What's [::-1]? Remember slicing: [start:stop:step]. When the step is -1, Python goes backwards. We leave start and stop empty, so it goes from end to beginning. It's elegant, but make sure you understand the manual way first

Let's try another approach: using a for loop with indexes

name = "Tommy"
reversed_str = ""
for i in range(len(name) - 1, -1, -1):
    reversed_str += name[i]
print(reversed_str)

Output ymmoT

range(len(name) - 1, -1, -1) means: start at the last index, go down to 0, step by -1. So for "Tommy" (length 5), we go through indexes 4, 3, 2, 1, 0

What about reversing words in a sentence, not individual characters?

sentence = "I love Vice City"
words = sentence.split(" ")
reversed_words = words[::-1]
result = " ".join(reversed_words)
print(result)

Output City Vice love I

.join() is the opposite of .split(). " ".join(["a", "b", "c"]) gives us "a b c". We split by space, reversed the list, and joined back with spaces

Mission: Decode Transmission

A garbled transmission just arrived. The crew suspects it was sent backwards, so you need to flip it two ways and see which one makes sense.

  1. Write a function reverse_text(text) that returns the text reversed character by character, using a loop (don't use [::-1]).
  2. Read the transmission, then print Reversed: followed by the character-reversed text.
  3. Also reverse the order of the words (split into words, reverse the list, join back with spaces) and print Word order: followed by the result.

Input:

  • the transmission, a line of words separated by spaces

Output: two lines: the character-reversed text, then the word-order-reversed text.

Example

If the user types

navigation system online

the program should print

Reversed: enilno metsys noitagivan
Word order: online system navigation