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p26_min_stack.py
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p26_min_stack.py
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"""
p26_min_stack
~~~~~~~~~~~~~~
问题:包含 min 函数的栈
定义栈的数据结构,在该类型中实现一个能够得到栈最小元素的 min 函数,
且调用 min, push, pop 的时间复杂度均为 O(1)
:copyright: (c) 2017 by 0xE8551CCB.
:license: MIT, see LICENSE for more details.
"""
from collections import deque, namedtuple
Element = namedtuple('Element', 'val, min')
class Stack(object):
def __init__(self):
self._elements = deque()
def empty(self):
return len(self._elements) == 0
def pop(self):
if not self.empty():
return self._elements.pop().val
def push(self, x):
if self.empty():
e = Element(x, x)
else:
min_val = x if x < self.min() else self.min()
e = Element(x, min_val)
self._elements.append(e)
def min(self):
return self._top().min
def top(self):
return self._top().val
def _top(self):
if not self.empty():
return self._elements[-1]
return Element(None, None)
if __name__ == '__main__':
s = Stack()
s.push(1)
s.push(2)
s.push(0)
print(s.min())
s.push(-1)
print(s.min())
s.pop()
print(s.min())
s.pop()
print(s.min())
s.pop()
print(s.min())