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.

我用了两个栈

不知道有没有更好的方法

class MinStack {
    Stack<Integer> st = new Stack<Integer>();
    Stack<Integer> min = new Stack<Integer>();
    public void push(int x) {
        st.push(x);
        if(min.isEmpty()){
            min.push(x);
        }else{
            if(x<=min.peek())
                min.push(x);
        }
    }

    public void pop() {
        int tmp = st.peek();
        st.pop();
        if(tmp==min.peek())
            min.pop();
    }

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

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