设计一个支持 push,pop,top 操作,并能在常数时间内检索到最小元素的栈。
- push(x) -- 将元素 x 推入栈中。
- pop() -- 删除栈顶的元素。
- top() -- 获取栈顶元素。
- getMin() -- 检索栈中的最小元素。
方案一:时间复杂度O(n)
class MinStack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.stack = []
def push(self, x):
"""
:type x: int
:rtype: void
"""
self.stack.append(x)
def pop(self):
"""
:rtype: void
"""
self.stack.pop()
def top(self):
"""
:rtype: int
"""
return self.stack[-1]
def getMin(self):
"""
:rtype: int
"""
return min(self.stack)
方案二:时间复杂度O(1)
class MinStack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.stack = []
self.min_stack = []
def push(self, x):
"""
:type x: int
:rtype: void
"""
self.stack.append(x)
if len(self.min_stack) == 0 or x <= self.min_stack[-1]:
self.min_stack.append(x)
def pop(self):
"""
:rtype: void
"""
if len(self.stack) != 0:
if len(self.min_stack) != 0 and self.stack[-1] == self.min_stack[-1]:
self.min_stack.pop()
self.stack.pop()
def top(self):
"""
:rtype: int
"""
return self.stack[-1]
def getMin(self):
"""
:rtype: int
"""
return self.min_stack[-1]