包含min函数的栈

定义栈的数据结构，请在该类型中实现一个能够得到栈最小元素的min函数。

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import java.util.Stack;

public class Solution {

    Stack<Integer> s1 = new Stack<>();
    Stack<Integer> s2 = new Stack<>();
    public void push(int node) {
        s1.push(node);
        if(s2.isEmpty() || s2.peek() > node)
            s2.push(node);
        else
            s2.push(s2.peek());
    }

    public void pop() {
        s1.pop();
        s2.pop();
    }

    public int top() {
        return s1.peek();
    }

    public int min() {
        return s2.peek();
    }
}