MinStack

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.

class MinStack {
    private Stack<Integer> stack;
    private Stack<Integer> min;  //存储最小数的栈

    public MinStack() {
        stack = new Stack<Integer>();
        min = new Stack<Integer>();
    }

    public void push(int x) {
        
        if (min.isEmpty() || min.peek()>=x)
            min.push(x);
        stack.push(x);
    }

    public void pop() {
        if (stack.peek().equals(min.peek()))
            min.pop();
        stack.pop();
    }

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

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