#+ANKI_DECK: study_deck_02
* TODO 0155. Min Stack :medium:
:PROPERTIES:
:NEETCODE: [[file:../../roadmap.org::*0155. Min Stack][0155. Min Stack]]
:END:

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Implement the ~MinStack~ class:

 - ~MinStack()~ initializes the stack object.

 - ~void push(int val)~ pushes the element ~val~ onto the stack.

 - ~void pop()~ removes the element on the top of the stack.

 - ~int top()~ gets the top element of the stack.

 - ~int getMin()~ retrieves the minimum element in the stack.

You must implement a solution with ~O(1)~ time complexity for each function.

*Example 1:*


#+begin_src
Input
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

Output
[null,null,null,null,-3,null,0,-2]

Explanation
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); // return -3
minStack.pop();
minStack.top();    // return 0
minStack.getMin(); // return -2
#+end_src


*Constraints:*

 - ~-2^{31} <= val <= 2^{31} - 1~

 - Methods ~pop~, ~top~ and ~getMin~ operations will always be called on *non-empty* stacks.

 - At most ~3 * 10^{4}~ calls will be made to ~push~, ~pop~, ~top~, and ~getMin~.

** TODO Approach
Write your approach here.

** TODO Python
#+begin_src python
class MinStack:

    def __init__(self):
        

    def push(self, val: int) -> None:
        

    def pop(self) -> None:
        

    def top(self) -> int:
        

    def getMin(self) -> int:
        


# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(val)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()
#+end_src

** TODO C++
#+begin_src cpp
class MinStack {
public:
    MinStack() {
        
    }
    
    void push(int val) {
        
    }
    
    void pop() {
        
    }
    
    int top() {
        
    }
    
    int getMin() {
        
    }
};

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack* obj = new MinStack();
 * obj->push(val);
 * obj->pop();
 * int param_3 = obj->top();
 * int param_4 = obj->getMin();
 */
#+end_src