# coding: utf-8
# # Sorting a list
# ## Swapping
# In order to sort a list, one of the most common operations to be done is swapping (exchanging) two elements.
# Examine the function defined below, and **run the code to define the function.**
#
# ##### Questions:
# * What is the name of the function? The name of the functions is Swap.
# * How many parameters does it have? It has 3 parameters. ‘Items’, ‘i’, and ‘j’.
# Swaps two elements in the list named items
# at positions i and j.
def swap(items,i,j):
temp = items[i]
items[j] = items[i]
items[i] = temp
# Before running the code below, **predict the output**. Then run the code and see if you were correct.
# In[ ]:
myList = [5, 10, 15, 20, 25, 30]
swap(myList, 1, 4)
print(myList)
# Now **modify the above code** to swap the first and last elements of myList.
# ## Bubble sort
# We now define a `bubbleSort` function that does an in-place sort of the list called `items`.
#There is no need to return a new list, because the function actually changes the original list.
#**Run the code to define the function.** There will not be any output.
# In[ ]:
def bubbleSort(items):
fullySorted = False
while not fullySorted: #outer loop
print(items)
i = len(items) – 1 #len() gets length, start at end of list
fullySorted = True
while i > 0: #inner loop, stop at top of list
if items[i] < items[i-1]:=”” #if=”” two=”” neighbouring=”” items=”” out=”” of=””>
swap(items,i,i-1) #use our swap function to swap them
fullySorted = False #list may not yet be sorted
i = i – 1 #decrement i
# #### Testing bubble sort
# If you want to see some output, you need to call the function, and pass in an argument to be used as the list `items`.
#**Run the code below** to call the function.
# In[ ]:
otherList = [395,2,-4,20,47,200,-50,-12] #a list for testing
print(‘Before sorting:’, otherList)
bubbleSort(otherList)
print(‘After sorting:’, otherList)
# ##### Questions:
# * What are the contents of `otherList` after a single iteration of the outer loop of `bubbleSort`?
# * How many iterations of the outer loop happen when sorting `otherList`?
# * Then run both blocks of code (the def block and the test block) again.
# * Examine the output to answer the question about iterations.
# * Now create a new list below, with 8 elements, called `yourList` — a list where you think you can get `bubbleSort` to stop early (do fewer iterations). How many times did the outer loop run for `yourList`?
# In[ ]:
yourList = [] #fill in this list with 8 elements separated by commas
print(‘Before sorting:’, yourList)
bubbleSort(yourList)
print(‘After sorting:’, yourList)
# ## Selection sort
# Recall selection sort from class. You will write your own version of the selection sort function.
#Remember, we already defined a `swap` function at the beginning of the notebook.
#Below is another function you will need for selection sort, called `minIndexAfter`.
#This function returns the index of the minimum element in `items` between `startPos` and the end of the list.
#**Run the code** to define the function.
# In[ ]:
def minIndexAfter(items, startPos):
minIndex = startPos
i = startPos + 1
while(i <>
if(items[i] <>
minIndex = i
i = i + 1
return minIndex
# Define a function called `selectionSort` below. In the body of the function, you will need to call the `swap` function and the `minIndexAfter` function.
# In[ ]:
#define selectionSort here:
# Use the following code to test your `selectionSort` function.
# In[ ]:
items = [395,2,-4,20,47,200,-50,-12
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