class MinStack {

public:

    struct Node {

        int nNum;

        int nMinNum;

        Node* pNext;

        Node() {

            pNext = nullptr;

        }

    };

    /** initialize your data structure here. */

    MinStack() {

        m_pHead = nullptr;

    }

    ~MinStack() {

        while(m_pHead != nullptr) {

            Node* pTmp = m_pHead;

            m_pHead = m_pHead->pNext;

            delete pTmp;

            pTmp = nullptr;

        }

    }

    void push(int x) {

        if(m_pHead == nullptr) {

            m_pHead = new Node;

            m_pHead->pNext = nullptr;

            m_pHead->nMinNum = x;

        }

        else {

            Node* pTmp = new Node;

            pTmp->nMinNum = m_pHead->nMinNum;

            pTmp->pNext = m_pHead;

            m_pHead = pTmp;

            if(m_pHead->nMinNum > x) {

                m_pHead->nMinNum = x;

            }

        }

        m_pHead->nNum = x;

    }

    void pop() {

        if(m_pHead != nullptr) {

            Node* pTmp = m_pHead;

            m_pHead = m_pHead->pNext;

            delete pTmp;

            pTmp = nullptr;

        }

    }

    int top() {

        if(m_pHead != nullptr) {

            return m_pHead->nNum;

        }

        return ;

    }

    int getMin() {

        return m_pHead->nMinNum;

    }

protected:

    Node* m_pHead;

};