题解 | 【模板】栈的操作

import sys

input = sys.stdin.read
data = input().split()
# print(data)
# ['7', 'push', '1', 'push', '2', 'size', 'query', 'pop', 'pop', 'query']

n = int(data[0])
stack = []
index = 1
output_lines = []

for _ in range(n):
    op = data[index]; index += 1

    if op == 'push':
        x = data[index]; index += 1
        stack.append(x)

    elif op == 'size':
        print(len(stack))
    
    elif op == 'query':
        if stack:
            print(stack[-1])
        else:
            print("Empty")
    
    elif op == 'pop':
        if stack:
            stack.pop()
        else:
            print("Empty")