目录
232.用栈实现队列
链接
相当于用两个stack将队列的元素顺序颠倒了一遍。
class MyQueue:
def __init__(self):
self.stack_in = []
self.stack_out = []
def push(self, x: int) -> None:
self.stack_in.append(x)
def pop(self) -> int:
if self.stack_out:
return self.stack_out.pop()
else:
for i in range(len(self.stack_in)):
self.stack_out.append(self.stack_in.pop())
return self.stack_out.pop()
def peek(self) -> int:
res = self.pop()
self.stack_out.append(res)
return res
def empty(self) -> bool:
return not(self.stack_in or self.stack_out)
225. 用队列实现栈
链接
class MyStack:
def __init__(self):
self.que = deque()
def push(self, x: int) -> None:
self.que.append(x)
def pop(self) -> int:
if self.empty():
return None
else:
for i in range(len(self.que) - 1):
self.push(self.que.popleft())
return self.que.popleft()
def top(self) -> int:
if self.empty():
return None
else:
return self.que[-1]
def empty(self) -> bool:
return len(self.que) == 0
