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

public class MinStack {

    /** initialize your dat_st structure here. */
    Stack<Integer>  dat_st     = new Stack<>();
    Stack<Integer>  min_st = new Stack<>();

    public MinStack() {
        dat_st.push(-1);
        min_st.push(Integer.MAX_VALUE);
    }

    public void push(int x) {
        dat_st.push(x);
        if(x <= min_st.peek())
            min_st.push(x);
    }

    public void pop() {

        int x = dat_st.pop();
        if(x == min_st.peek())
            min_st.pop();
    }

    public int top() {
        return dat_st.peek();
    }

    public int getMin() {
        return min_st.peek();
    }
}