Need Help with Python Assignment Involving Lists, Finding Minimum Value, Insert and Delete

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  • V

    Hi Everyone,

    I was wondering if somebody could guide me in the right direction for the following assignment.
    I am lost and any help would be greatly appreciated! Thank you in advanced.

    Magic List is a special type of list L in which the elements are arranged according to the following
    properties :

    1. The first element of the list is always 0 (L[0] = 0).
    2. For each index i (>= 1), L[i] <= L[2i] and L[i] <= L[2i+1].
    3. For each index i (>= 1), L[i/2] is called the parent of L[i], and L[2i], L[2i+1] are called the children of
      L[i].
    4. L[1] has no parent.
      In this list, all the elements besides the first one are called magic elements. The size of Magic List is
      the number of magic elements in the list. Observe that L[1] will be the smallest magic element in list
      (Due to point 2. above).
      A class called MagicList has been given to you (inside MagicList.py). You have to complete the
      following functions inside the file :
    5. findMin
      Complete the findMin function and return the smallest magic element in the Magic List. If there are
      no magic elements (i.e. size of Magic List is zero), then return None.
    6. insert
      Complete the insert function and return the modified list. To insert an element in the Magic List, first
      append the element to the end of the list. Start at last element and keep comparing with parent
      L[i/2]. If parent is larger, swap the parent and the element. Keep doing this till parent is smaller, or
      the element has no parent.
    7. deleteMin
      Complete the deleteMin function, delete the smallest magic element in the Magic List, and return
      the modified list. To delete the minimum element, swap the minimum element (E1) with the last
      element (E2) and remove the last element. Keep comparing E2 with children L[2i] and L[2i+1] and
      swap with the smaller child. Keep doing this till both children are greater than E2 or E2 has no more
      children.
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  • avan

    OK. I saw a couple of things slightly off such as looping starting at 0 instead of 1. There were was at least one other mistake I have notices but it would take too long to dissect it all.

    Here is the code that I got but like I said I am not 100% confident it would pass more advanced tests.

    class MagicList:
  def __init__(self):
    self.data = [0]
	
  def findMin(self):
    M = self.data
    ''' you need to find and return the smallest
      element in MagicList M.
      Write your code after this comment.
    '''
    # Make sure there is at least one element
    if(len(M) < 1):
      return None
    # Initialize i to 1
    # Temporarily set the min to the first value e.g. M[i]
    i = 1
    min = M[i]
    # Iterate over the list M
    while (i < len(M)):
      # check if the current element in the iteration is smaller than min
      if (M[i] < min):
        # New min found, update min
        min = M[i]
      # update i by adding 1
      i += 1
    return min
	
  def insert(self, E):
    M = self.data
    ''' you need to insert E in MagicList M, so that
      properties of the MagicList are satisfied. 
      Return M after inserting E into M.
      Write your code after this comment.
      
      # Algorithm  
      1) first append the element to the end of the list. 
      2) Start at last element and keep comparing with parent L[i/2]. 
      3) If parent is larger, swap the parent and the element. 
      4) Keep doing this till parent is smaller, or
        # the element has no parent.
    '''
    # Step 1 
    # Add element to end of the list using append
    M.append(E)
    # Step 2
    # Initialize size to the length of M e.g. size = len(M) 
    size = len(M)
    # Subtract one from i
    i = size - 1
    # Initialize parent_i to i / 2
    parent_i = int(i / 2)
    # while i is greater than 0
    while(i > 0):
      # set parent_element to M[parent_i]
      parent_element = M[parent_i]
      # Step 3
      # if E is less than parent_element 
      if (E < parent_element):
        # Swap with parent (M[parent_i] --> E and M[i] --> parent_element)
        M[parent_i] = E
        M[i] = parent_element
        # update i and parent_i, i --> parent_i and parent_i --> parent_i / 2
        i = parent_i
        parent_i = int(parent_i/2)
      else:
        # Stop here. Break from while loop and return list and 
        break
    # Return List at the End of While Loop
    return M  

  def deleteMin(self):
    M = self.data
    ''' you need to delete the minimum element in
      MagicList M, so that properties of the MagicList
      are satisfied. Return M after deleting the 
      minimum element.
      Write your code after this comment.
    
    # Algorithm
    To delete the minimum element, 
    1) swap the minimum element (E1) with the last
    element (E2) and remove the last element. 
    2) Keep comparing E2 with children L[2i] and L[2i+1] and swap with the smaller child. Keep doing this till both children are greater than E2 or E2 has no more children.
    '''
    # Step 1 Set min to self.findMin()
    min = self.findMin()
    # Set i to 0
    i = 0
    # Iterate over M until i >= len(M)
    while(i < len(M)):
      # Check if M[i] is min
      if(M[i] == min):
        # Found minimum, now set location of min to the last element (hint: use M[-1])
        # No swap per se.  
        # Set M[i] to last element
        M[i] = M[-1]
        # Set E2 to M[i]
        E2 = M[i]
        # Delete last element (use pop())
        M.pop()
        # Another while loop this time run while i is less than len(M)
        # and 2*1 is less than len(M) and 2*1+1 is less than len(M)
        while(i < len(M) and (2*i < len(M)) and (2*i+1 < len(M))):
          # Step 2
          # Check if E2 is less than its child M[2*1]
          if(E2 < M[2*i]):
            # Complete swap with this child
            child = M[i*2]
            M[i*2] = E2
            M[i] = child
          # Else Check if E2 is less than its other child M[2*1+1]
          elif(E2 < M[2*i+1]):
            # Complete swap with this child
            child = M[i*2+1]
            M[i*2+1] = E2
            M[i] = child
          # Increase by a factor of 2 so i *= 2
          i *= 2    
        # Stop the outer loop  
        break   
      # Increase i by 1
      i += 1
    return M    


M = MagicList()
M.insert(4)
M.insert(3)
M.insert(5)
x = M.findMin()
if x == 3 :
	print("testcase 1 : Passed")
else :
	print("testcase 1 : Failed")
	
'''deleteMin and findMin'''
M.deleteMin()
x = M.findMin()
if x == 4 :
	print("testcase 2 : Passed")
else :
	print("testcase 2 : Failed")
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  • avan

    Hi @vvv003 Can we see MagicList.py?

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  • V

    @avan this is magiclist.py please help!!

    class MagicList :
	def __init__(self):
		self.data = [0]
	
	def findMin(self):
		M = self.data
		''' you need to find and return the smallest
			element in MagicList M.
			Write your code after this comment.
		'''
	
	def insert(self, E):
		M = self.data
		''' you need to insert E in MagicList M, so that
			properties of the MagicList are satisfied. 
			Return M after inserting E into M.
			Write your code after this comment.
		'''
	
	def deleteMin(self):
		M = self.data
		''' you need to delete the minimum element in
			MagicList M, so that properties of the MagicList
			are satisfied. Return M after deleting the 
			minimum element.
			Write your code after this comment.
		'''

    if name == "main" :
    '''Here are a few test cases'''

    '''insert and findMin'''
M = MagicList()
M.insert(4)
M.insert(3)
M.insert(5)
x = M.findMin()
if x == 3 :
	print("testcase 1 : Passed")
else :
	print("testcase 1 : Failed")
	
'''deleteMin and findMin'''
M.deleteMin()
x = M.findMin()
if x == 4 :
	print("testcase 2 : Passed")
else :
	print("testcase 2 : Failed")
    0
  • avan

    I think I got it! Test cases are on the light side so I don't know if it is a correct solution for sure.

    However before I give you the complete code I would like to try this psudo code version first. Let me know what you struggle with or what parts are still unclear.

    I really want to help you but I need a little bit of engagement from you before I give you the code. I hope you understand.

    class MagicList:
  def __init__(self):
    self.data = [0]
	
  def findMin(self):
    M = self.data
    ''' you need to find and return the smallest
      element in MagicList M.
      Write your code after this comment.
    '''
    # Make sure there is at least one element
    if(...):
      return None
    # Initialize i to 1
    # Temporarily set the min to the first value e.g. M[i]
    i ..
    min...
    # Iterate over the list M
    while...:
      # check if the current element in the iteration is smaller than min
      if ...:
        # New min found, update min
        min...
      # update i by adding 1
      i ...
    #return min
    return ...
	
  def insert(self, E):
    M = self.data
    ''' you need to insert E in MagicList M, so that
      properties of the MagicList are satisfied. 
      Return M after inserting E into M.
      Write your code after this comment.
      
      # Algorithm  
      1) first append the element to the end of the list. 
      2) Start at last element and keep comparing with parent L[i/2]. 
      3) If parent is larger, swap the parent and the element. 
      4) Keep doing this till parent is smaller, or
        # the element has no parent.
    '''
    # Step 1 
    # Add element to end of the list using append
    M...
    # Step 2
    # Initialize size to the length of M e.g. size = len(M) 
    size...
    # Subtract one from i
    i...
    # Initialize parent_i to i / 2
    parent_i...
    # while i is greater than 0
    while...
      # set parent_element to M[parent_i]
      parent_element....
      # Step 3
      # if E is less than parent_element 
      if ...:
        # Swap with parent (M[parent_i] --> E and M[i] --> parent_element)
        M...
        M[i]...
        # update i and parent_i, i --> parent_i and parent_i --> parent_i / 2
        i ...
        parent_i...
      else:
        # Stop here. Break from while loop and return list and 
        break
    # Return List at the End of While Loop
    return M  

  def deleteMin(self):
    M = self.data
    ''' you need to delete the minimum element in
      MagicList M, so that properties of the MagicList
      are satisfied. Return M after deleting the 
      minimum element.
      Write your code after this comment.
    
    # Algorithm
    To delete the minimum element, 
    1) swap the minimum element (E1) with the last
    element (E2) and remove the last element. 
    2) Keep comparing E2 with children L[2i] and L[2i+1] and swap with the smaller child. Keep doing this till both children are greater than E2 or E2 has no more children.
    '''
    # Step 1 Set min to self.findMin()
    min ...
    # Set i to 0
    i ...
    # Iterate over M until i >= len(M)
    while....
      # Check if M[i] is min
      if...
        # Found minimum, now set location of min to the last element (hint: use M[-1])
        # No swap per se.  
        # Set M[i] to last element
        M[i]....
        # Set E2 to M[i]
        E2...
        # Delete last element (use pop())
        M...
        # Another while loop this time run while i is less than len(M)
        # and 2*1 is less than len(M) and 2*1+1 is less than len(M)
        while...
          # Step 2
          # Check if E2 is less than its child M[2*1]
          if....
            # Complete swap with this child
            child....
            M[i*2]...
            M[i]...
          # Else Check if E2 is less than its other child M[2*1+1]
          elif....
            # Complete swap with this child
            child....
            M[i*2+1]...
            M[i]....
          # Increase by a factor of 2 so i *= 2
          i *=...
        # Stop the outer loop  
        break   
      # Increase i by 1
      i ...
    return M
    0
  • V

    @avan testcase : failed
    what should i do?

    Here is my code:

    class MagicList:
  def __init__(self):
    self.data = [0]
	
  def findMin(self):
    M = self.data
    ''' you need to find and return the smallest
      element in MagicList M.
      Write your code after this comment.
    '''
    if len(self.data) == 1:
      return None
    # Initialize i to 1
    # Temporarily set the min to the first value e.g. M[i]
    i = 1
    min = M[i]
    # Iterate over the list M
    length = len(M)
    for i in range(length):
      # check if the current element in the iteration is smaller than min
      if M[i] < min:
        # New min found, update min
        min = M[i] + 1
      # update i by adding 1
    #return min
    return min

  def insert(self, E):
    M = self.data
    ''' you need to insert E in MagicList M, so that
      properties of the MagicList are satisfied. 
      Return M after inserting E into M.
      Write your code after this comment.
      
      # Algorithm  
      1) first append the element to the end of the list. 
      2) Start at last element and keep comparing with parent L[i/2]. 
      3) If parent is larger, swap the parent and the element. 
      4) Keep doing this till parent is smaller, or
        # the element has no parent.
    '''
    # Step 1 
    # Add element to end of the list using append
    M.append(E)
    # Step 2
    # Initialize size to the length of M e.g. size = len(M) 
    size = len(M)
    # Subtract one from i
    i = len(M) - 1
    # Initialize parent_i to i / 2
    parent_i = i/2
    # while i is greater than 0
    while i>0:
      # set parent_element to M[parent_i]
      parent_element = M[int(parent_i)]
      # Step 3
      # if E is less than parent_element 
      if E < parent_element:
        # Swap with parent (M[parent_i] --> E and M[i] --> parent_element)
        M[int(parent_i)] = E
        M[i] = parent_element
        # update i and parent_i, i --> parent_i and parent_i --> parent_i / 2
        i = parent_i
        parent_i = parent_i / 2
      else:
        # Stop here. Break from while loop and return list and 
        break
    # Return List at the End of While Loop
    return M  

  def deleteMin(self):
    M = self.data
    ''' you need to delete the minimum element in
      MagicList M, so that properties of the MagicList
      are satisfied. Return M after deleting the 
      minimum element.
      Write your code after this comment.
    
    # Algorithm
    To delete the minimum element, 
    1) swap the minimum element (E1) with the last
    element (E2) and remove the last element. 
    2) Keep comparing E2 with children L[2i] and L[2i+1] and swap with the smaller child. Keep doing this till both children are greater than E2 or E2 has no more children.
    '''
    # Step 1 Set min to self.findMin()
    min = self.findMin()
    # Set i to 0
    i = 0
    # Iterate over M until i >= len(M)
    length = len(M)
    for i in range(i >= len(M)):
      # Check if M[i] is min
      if M[i] == min:
        # Found minimum, now set location of min to the last element (hint: use M[-1])
        # No swap per se.  
        # Set M[i] to last element
        M[i] = M[-1]
        # Set E2 to M[i]
        E2 = M[i]
        # Delete last element (use pop())
        M.pop()
        # Another while loop this time run while i is less than len(M)
        # and 2*1 is less than len(M) and 2*1+1 is less than len(M)
        while i < len(M) and 2*1 < len(M) and 2*1+1 < len(M):
          # Step 2
          # Check if E2 is less than its child M[2*1]
          if E2 < M[2*1]:
            # Complete swap with this child
            child = M[i*2]
            M[i*2] = M[i]
            M[i] = child
          # Else Check if E2 is less than its other child M[2*1+1]
          elif E2 < M[2*1+1]:
            # Complete swap with this child
            child = M[i*2+1]
            M[i*2+1] = M[i]
            M[i] = child
          # Increase by a factor of 2 so i *= 2
          i *= 2
        # Stop the outer loop  
        break   
      # Increase i by 1
      i = i + 1
    return M

    if name == "main" :
    '''Here are a few test cases'''

      '''insert and findMin'''
  M = MagicList()
  M.insert(4)
  M.insert(3)
  M.insert(5)
  x = M.findMin()
  if x == 3 :
    print("testcase 1 : Passed")
  else :
    print("testcase 1 : Failed")

  M.deleteMin()
  x = M.findMin()
  if x == 4 :
    print("testcase 2 : Passed")
  else :
    print("testcase 2 : Failed")
    0
  • avan

    OK. I saw a couple of things slightly off such as looping starting at 0 instead of 1. There were was at least one other mistake I have notices but it would take too long to dissect it all.

    Here is the code that I got but like I said I am not 100% confident it would pass more advanced tests.

    class MagicList:
  def __init__(self):
    self.data = [0]
	
  def findMin(self):
    M = self.data
    ''' you need to find and return the smallest
      element in MagicList M.
      Write your code after this comment.
    '''
    # Make sure there is at least one element
    if(len(M) < 1):
      return None
    # Initialize i to 1
    # Temporarily set the min to the first value e.g. M[i]
    i = 1
    min = M[i]
    # Iterate over the list M
    while (i < len(M)):
      # check if the current element in the iteration is smaller than min
      if (M[i] < min):
        # New min found, update min
        min = M[i]
      # update i by adding 1
      i += 1
    return min
	
  def insert(self, E):
    M = self.data
    ''' you need to insert E in MagicList M, so that
      properties of the MagicList are satisfied. 
      Return M after inserting E into M.
      Write your code after this comment.
      
      # Algorithm  
      1) first append the element to the end of the list. 
      2) Start at last element and keep comparing with parent L[i/2]. 
      3) If parent is larger, swap the parent and the element. 
      4) Keep doing this till parent is smaller, or
        # the element has no parent.
    '''
    # Step 1 
    # Add element to end of the list using append
    M.append(E)
    # Step 2
    # Initialize size to the length of M e.g. size = len(M) 
    size = len(M)
    # Subtract one from i
    i = size - 1
    # Initialize parent_i to i / 2
    parent_i = int(i / 2)
    # while i is greater than 0
    while(i > 0):
      # set parent_element to M[parent_i]
      parent_element = M[parent_i]
      # Step 3
      # if E is less than parent_element 
      if (E < parent_element):
        # Swap with parent (M[parent_i] --> E and M[i] --> parent_element)
        M[parent_i] = E
        M[i] = parent_element
        # update i and parent_i, i --> parent_i and parent_i --> parent_i / 2
        i = parent_i
        parent_i = int(parent_i/2)
      else:
        # Stop here. Break from while loop and return list and 
        break
    # Return List at the End of While Loop
    return M  

  def deleteMin(self):
    M = self.data
    ''' you need to delete the minimum element in
      MagicList M, so that properties of the MagicList
      are satisfied. Return M after deleting the 
      minimum element.
      Write your code after this comment.
    
    # Algorithm
    To delete the minimum element, 
    1) swap the minimum element (E1) with the last
    element (E2) and remove the last element. 
    2) Keep comparing E2 with children L[2i] and L[2i+1] and swap with the smaller child. Keep doing this till both children are greater than E2 or E2 has no more children.
    '''
    # Step 1 Set min to self.findMin()
    min = self.findMin()
    # Set i to 0
    i = 0
    # Iterate over M until i >= len(M)
    while(i < len(M)):
      # Check if M[i] is min
      if(M[i] == min):
        # Found minimum, now set location of min to the last element (hint: use M[-1])
        # No swap per se.  
        # Set M[i] to last element
        M[i] = M[-1]
        # Set E2 to M[i]
        E2 = M[i]
        # Delete last element (use pop())
        M.pop()
        # Another while loop this time run while i is less than len(M)
        # and 2*1 is less than len(M) and 2*1+1 is less than len(M)
        while(i < len(M) and (2*i < len(M)) and (2*i+1 < len(M))):
          # Step 2
          # Check if E2 is less than its child M[2*1]
          if(E2 < M[2*i]):
            # Complete swap with this child
            child = M[i*2]
            M[i*2] = E2
            M[i] = child
          # Else Check if E2 is less than its other child M[2*1+1]
          elif(E2 < M[2*i+1]):
            # Complete swap with this child
            child = M[i*2+1]
            M[i*2+1] = E2
            M[i] = child
          # Increase by a factor of 2 so i *= 2
          i *= 2    
        # Stop the outer loop  
        break   
      # Increase i by 1
      i += 1
    return M    


M = MagicList()
M.insert(4)
M.insert(3)
M.insert(5)
x = M.findMin()
if x == 3 :
	print("testcase 1 : Passed")
else :
	print("testcase 1 : Failed")
	
'''deleteMin and findMin'''
M.deleteMin()
x = M.findMin()
if x == 4 :
	print("testcase 2 : Passed")
else :
	print("testcase 2 : Failed")
    0
  • avan

    @vvv003 Do you mind selecting my last answer as the correct one if it worked for you? Thank you!

    0