716. max stack

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Leetcode
Stack
Design

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:

• $-1e^7 &lt;= x$ <= 1e^7$
• Number of operations won't exceed 10000.
• The last four operations won't be called when stack is empty.

分析¶