[LeetCode] Min Stack

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

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

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 Stack Data Structure

 

class MinStack {
    private:
        vector<int> m_data;
        vector<int> m_min;
    public:
        void push(int x) {
            if(m_data.size() == 0)
                m_min.push_back(x);
            else
            {
                if(m_min[m_min.size() - 1] > x)
                    m_min.push_back(x);
                else
                    m_min.push_back(m_min[m_min.size() - 1]);
            }   
            m_data.push_back(x);
        }   

        void pop() {
            m_data.pop_back();
            m_min.pop_back();
        }   

        int top() {
            int size = m_data.size();
            if(size > 0)
                return m_data[size - 1]; 
            else
                return -1; 
        }   

        int getMin() {
            int size = m_min.size();
            if(size > 0)
                return m_min[size - 1];
            else
                return -1;

        }
};