Question

1. Using Python list tools, create the standard stack (push, pop) and queue (enqueue, dequeue) operations
2. Counting Letter Challenge: Create a function that...
   1. Takes in a string as parameter
   2. Counts how often each letter appears in the string
   3. Returns a dictionary with the counts
   4. BONUS: make it so lowercase and uppercase letter count for the same letter

Answer 1

STACK IMPLEMENTATION USING LIST:

# class to represent the stack using list
class Stack:

     # constructor to initialize the object
     def __init__(self):
         self.item_lst = []

     # method to push an element into the stack
     def push(self, item):
         self.item_lst.append(item)

     # method to remove the top element from the stack
     def pop(self):
         return self.item_lst.pop()

     # method to retrieve the top element of the stack
     def peek(self):
         return self.item_lst[len(self.item_lst)-1]

     # method to find the size of the stack
     def size(self):
         return len(self.item_lst)

     # method to find the emptiness of the stack
     def isEmpty(self):
         return self.item_lst == []

# testing
if __name__=='__main__':

    # creating stack object
    s=Stack()

    # checking for empty
    print(s.isEmpty())

    # adding elements into the stack
    s.push(44)
    s.push(55)
    s.push(60)

    # displaying the size of the stack
    print(s.size())  
    s.push(4.55)

    # calling various functions of the stack
    print(s.pop())  
    print(s.size())
    print(s.peek())

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QUEUE IMPLEMENTATION USING LIST:

# class to represent the QUEUE using list
class Queue:

    # constructor to initialize the object
    def __init__(self):
        self.item_lst = []

    # method to add a element in the queue
    def enqueue(self, i):
        self.item_lst.insert(0,i)

    # method to remove a element from the queue
    def dequeue(self):
        return self.item_lst.pop()

    # method to find the size of the queue
    def size(self):
        return len(self.item_lst)

    # method to find the emptiness of the queue
    def isEmpty(self):
        return self.item_lst == []
    
# testing
if __name__=='__main__':

    # creating queue object
    q=Queue()

    # adding elements to the queue
    q.enqueue(47)
    q.enqueue(52)
    q.enqueue(62)

    # displaying the size of the queue
    print(q.size())

    # removing the first element from the queue
    print(q.dequeue())
    q.enqueue(50)

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CODE FOR LETTER COUNT FUNCTION:

# function to count letters in a string
def count_letter(s):

    # dictionary to store the letter count
    d={}

    # looping through every character in the string
    for c in s:

        # changing to lowercase
        c=c.lower()

        # adding the character to the dictionary
        if c not in d:
            d[c]=1
        else:
            d[c]+=1

    # returning the dictionary
    return d

# testing
if __name__=='__main__':

    print(count_letter('python'))
    print(count_letter('Python ProgramMing'))

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