Stack and Queue

Stack, follow the LIFO (Last in First out) principle. Imagine like a one-way slot, the first one to come in, come out last and vice versa.

stack operation

class Stack:
    def __init__(self):
        self.l = []

    def push(self, i):
        self.l.append(i)
        print("push :", self.l)

    def pop(self):
        self.l.pop()
        print("pop :",self.l)

    def peek(self):
        print("Last chara :", self.l[(len(self.l) - 1)])
        print("Stack :",self.l)

    def is_empty(self):
        return len(self.l) == 0

    def size(self):
        print("Length :", len(self.l))

    def __str__(self):
        return str(self.l)

Queue, follow the FIFO (First in First out) principle. Imagine a queue when you go and buy something.

class Queue:  
    def __init__(self): 
        self.s1 = [] 
        self.s2 = [] 
  
    def enQueue(self, x): 
        while len(self.s1) != 0:  
            self.s2.append(self.s1[-1])  
            self.s1.pop() 
        self.s1.append(x)  
  
        while len(self.s2) != 0:  
            self.s1.append(self.s2[-1])  
            self.s2.pop() 
  
    def deQueue(self): 
        if len(self.s1) == 0:  
            print("Q is Empty") 
      
        x = self.s1[-1]  
        self.s1.pop()  
        return x

Conclusion

We can implement stack and queue to many real-world cases. By, understanding how to use them allow us to solve a lot more problems.