clean up indexing chapters

Author: Kristian Rother

challenges/ctree.rst

@@ -1,5 +1,5 @@
-Christmas Tree
-==============
+Star Tree
+=========
 
 **🎯 Write a program that outputs the following image:**
 
@@ -11,3 +11,8 @@ Christmas Tree
      *******
     *********
    ***********
+
+.. hint::
+
+   You don't need to come up with an elegant solution right aways.
+   For your first implementation, a straightforward solution is good enough.

data_structures/dictionaries.md

@@ -11,6 +11,8 @@ area    topic
 ⚙       define a dictionary
 ⚙       look up values of a dictionary
 🔀      iterate through a list of dictionary keys
+🔀      use lists as dictionary values
+🐞      fix errors in dictionary definitions
 🐞      fix index errors
 ======= ====================================
 
@@ -73,9 +75,40 @@ Improve the receipt assistant from the previous chapter
 so that it uses a dictionary of prices.
 
 
+Exercise 5: Traveler
+--------------------
+
+The following program allows you to travel from one city to the next.
+Unfortunately, it contains **five bugs**. Find and fix them.
+
+.. code:: python3
+
+   cities = {
+       "New York": ["Tokyo", "Delhi", "London"],
+       "Poznan": ["London", "Berlin"],
+       "London": ["New York", "Poznan"]
+       "Berlin": ["Tokyo", "Poznan"],
+       "Tokyo": ["New York" "Berlin"],
+       "Delhi": ["Katmandu"]
+       }
+
+   location = "Berlin"
+   print "\nYour task: fly to Katmandu\n"
+
+   while location in cities and location == 'Katmandu':
+       print(f"You are in {location}")
+
+   print("There are flights to ", cities["location"])
+   location = input("Where would you like to travel?")
+
+   print("You have reached your destination")
+
+
 Reflection Questions
 --------------------
 
 -  How can you create a dictionary?
+-  What data types can you use as keys of a dictionary?
+-  What data types can you use as values of a dictionary?
 -  How can you modify values in a dictionary?
 -  Is it possible to run a for loop over a dictionary?

data_structures/indexing.rst

@@ -0,0 +1,114 @@
+
+Block Cipher
+============
+
+In this chapter you will:
+-------------------------
+
+======= ====================================
+area    topic
+======= ====================================
+🚀      implement a transposition cipher
+⚙       slice lists and strings
+💡      use the ``join`` method of the ``string`` data type
+🔀      use a loop variable for indexing
+======= ====================================
+
+
+Indexing and Slicing
+--------------------
+
+Strings and lists are both ordered sequences of elements.
+In both, you can address elements by their position.
+However, Python is counting differently than humans:
+
+.. figure:: indexing.png
+   :alt: Indexing
+
+
+Exercise 1: Indexing lists
+--------------------------
+
+What do the following expressions result in?
+
+.. code:: python3
+
+   numbers = [1, 4, 9, 16, 25, 36]
+
+   numbers[4]
+   movies[0]
+   movies[-1]
+   numbers[-3]
+
+
+Exercise 2: Slicing strings
+---------------------------
+
+What do the following commands result in?
+
+   name = "hello world"
+
+   name[5:]
+   name[5:10]
+   name[:10:2]
+   numbers[2:-2]
+   numbers[::2]
+
+
+Exercise 3: Decypher
+--------------------
+
+The following text contains an encrypted word:
+
+.. code:: python3
+
+   name = "CSAIPRALKAINACZEYLVOST"
+
+Print every second character, starting with the 2nds.
+
+
+Exercise 4: Slicing puzzle
+--------------------------
+
+Use the expressions to modify the list as indicated. Use each expression
+once.
+
+.. figure:: list_funcs1.png
+   :alt: list funcs exercise1
+
+   list funcs exercise1
+
+
+Exercise 5: Blocks
+------------------
+
+The following code is creating the first two blocks for a `transposition cipher <https://en.wikipedia.org/wiki/Transposition_cipher>`__ .
+Complete the code by creating the other two blocks as well.
+
+.. code:: python3
+
+   message = "MEETINGATDAWNATTHEBRIDGE"
+
+   block1 = message[0::4]
+   block2 = message[1::4]
+   ___
+   ___
+   encrypted = block1 + block2 + block3 + block4
+
+
+Exercise 6: Transposition Cipher
+--------------------------------
+
+Complete the program that encrypts a text using a transposition cipher:
+
+.. code:: python3
+
+   message = input("enter the text to encrypt: ")
+   encrypted = ""
+   for start in range(4):
+       ___
+
+Exercise 7: Decrypt
+-------------------
+
+Write a program to decrypt an encrypted message again.

first_steps/dictionaries.rst

@@ -36,8 +36,9 @@ First Steps
    first_steps/guess_the_number.rst
    first_steps/cypher.rst
    first_steps/bill.rst
-   first_steps/slideshow.rst
    first_steps/dictionaries.md
+   first_steps/indexing.rst
+   first_steps/slideshow.rst
 
 
 Tabular Data
@@ -46,7 +47,6 @@ Tabular Data
 .. toctree:: 
    :maxdepth: 1
 
-   data_structures/indexing.rst
    data_structures/tables.md
    tabular_data/readfile.md
    tabular_data/parsing.md