求助leet code 716 Max Stack

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 // this step should be 1 or 5? 不是很明白为什么是1. 前几步有两个5被push进去了， 只pop Max了一个 5 难道不是应该还留下一个 5吗
stack.peekMax(); -> 5
stack.pop(); -> 1
stack.top(); -> 5

楼主你标注的那一行，应该top就是1吧，之前popmax了一个最顶上的5，不难理解吧？

top() -- Get the element on the top.
[5]
[5, 1]
[5, 1, 5]
pop max 显然是最后一个5 -> [5, 1]
top就是1呗.

补充内容 (2019-4-28 07:13):
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.

我写过一段简单的分析，不知道你是否能看明白。
https://github.com/wisdompeak/Le ... esign/716.Max-Stack