Java学习-1

今天学了点Java构建最小栈的方法,采用的是链表存储其中的最小值以及当前节点的数值，在插入栈内新元素的时候进行对应的最小值比对，插入到private链表中。

class ListNode{
    public int val;
    public int min;
    public ListNode next;

    public ListNode(int val,int min,ListNode next){
        this.val=val;
        this.min=min;
        this.next=next;
    }
}

class MinStack {
    private ListNode head;
    public MinStack() {

    }
    private boolean empty(){
        return head==null;
    }
    
    public void push(int x) {
        if(empty()){
            head=new ListNode(x,x,null);
        }
        else{
            head=new ListNode(x,Math.min(head.min,x),head);
        }
    }
    
    public void pop() {
        if(empty()){
            throw new IllegalStateException("stack is empty!");
        }
        head=head.next;
    }
    
    public int top() {
        if(empty()){
            throw new IllegalStateException("stack is empty!");
        }
        return head.val;
    }
    
    public int getMin() {
        if(empty()){
            throw new IllegalStateException("stack is empty!");
        }
        return head.min;
    }
}