leetcode/stack.py at main · Lucasbritx/leetcode · GitHub

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class Node:
    def __init__(self, value):
        self.value = value
        self.next = None

class Stack:
    def __init__(self):
        self.top = None
        self._size = 0

    def push(self, item):
        new_node = Node(item)
        new_node.next = self.top
        self.top = new_node
        self._size +=1

    def pop(self):
        if self.top is None:
            raise IndexError("Empty stack")
        popped_node = self.top
        self.top = popped_node.next
        self._size -=1

        return popped_node.value

    def peek(self):
        if self.top is None:
            raise IndexError("Empty stack")
        return self.top.value

    def size(self):
        return self._size


stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
print(stack.pop()) # 3
print(stack.peek()) # 2
print(stack.size()) # 2
print(stack.pop()) # 2
print(stack.pop()) # 1
print(stack.pop()) # Error