155. 最小栈

class MinStack {
    private Stack<Integer> stack;
    private Stack<Integer> minStack;

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

    public void push(int val) {
        stack.push(val);
        if (minStack.isEmpty()||val<minStack.peek()){
            minStack.push(val);
        }else{
            minStack.push(minStack.peek());
        }
    }

    public void pop() {
        stack.pop();
        minStack.pop();
    }

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

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