# Min Stack Problem

## Description

LeetCode Problem 155.

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.

Example 1:

``````1
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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
``````

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.

## Sample C++ Code

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class MinStack {
public:
stack<int> st;
stack<int> minst;

MinStack() {

}

void push(int x) {
st.push(x);
int y;
if (!minst.empty()) {
y = minst.top();
minst.push(min(x, y));
} else {
minst.push(x);
}
}

void pop() {
st.pop();
minst.pop();
}

int top() {
if (st.empty())
return 0;
return st.top();
}

int getMin() {
if (minst.empty())
return 0;
return minst.top();
}
};
``````