原题
Design a max stack that supports push, pop, top, peekMax and popMax.
push(x) – Push element x onto stack.
pop() – Remove the element on top of the stack and return it.
top() – Get the element on the top.
peekMax() – Retrieve the maximum element in the stack.
popMax() – Retrieve the maximum element in the stack, and remove it. If you find more than one maximum elements, only remove the top-most one.
Example 1:
MaxStack stack = new MaxStack();
stack.push(5);
stack.push(1);
stack.push(5);
stack.top(); -> 5
stack.popMax(); -> 5
stack.top(); -> 1
stack.peekMax(); -> 5
stack.pop(); -> 1
stack.top(); -> 5
Note:
-1e7 <= x <= 1e7
Number of operations won’t exceed 10000.
The last four operations won’t be called when stack is empty.
解法
使用列表, 每次push时向列表左边添加元素.
代码
class MaxStack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.data = []
def push(self, x):
"""
:type x: int
:rtype: None
"""
self.data.insert(0, x)
def pop(self):
"""
:rtype: int
"""
return self.data.pop(0)
def top(self):
"""
:rtype: int
"""
return self.data[0]
def peekMax(self):
"""
:rtype: int
"""
return max(self.data)
def popMax(self):
"""
:rtype: int
"""
ans = max(self.data)
self.data.remove(ans)
return ans
# Your MaxStack object will be instantiated and called as such:
# obj = MaxStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.peekMax()
# param_5 = obj.popMax()