定义
只能从尾部加入或删除, 也就是后进先出(LIFO, last in first out).
栈的方法与实现:
push 压入元素
pop 返回最顶端元素
size 返回栈大小
方法
- 实现代码
#LIFO: last item we insert is the first we take out
class Stack:
#we represent the stack with the help of an array
def __init__(self):
self.stack = []
#check whether the stack is empty or not
def is_empty(self):
return self.stack == []
#pushing a new item onto the stack - O(1) running time
#append will put the item at the end of the list
def push(self, data):
self.stack.append(data)
#getting the last item we have inserted - O(1) running time
def pop(self):
#maybe there is no item on the stack
if self.is_empty():
raise Exception("Stack is empty...")
data = self.stack[-1]
del self.stack[-1]
return data
#getting the last item without removing it
def peek(self):
#maybe there is no item on the stack
if self.is_empty():
raise Exception("Stack is empty...")
return self.stack[-1]
def size_stack(self):
return len(self.stack)
if __name__ == "__main__":
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
print(stack.size_stack())
print("Popped: ", stack.pop())
print("Popped: ", stack.pop())
print(stack.size_stack())
print("Peek:", stack.peek())
print(stack.size_stack())
题目
不存在边界条件
持续。。。
