单双链表及其反转-堆栈诠释

// 按值传递、按引用传递
// 从堆栈角度解释链表节点
// 以堆栈视角来看链表反转
public class ListReverse {

	public static void main(String[] args) {
		// int、long、byte、short
		// char、float、double、boolean
		// 还有String
		// 都是按值传递
		int a = 10;
		f(a);
		System.out.println(a);

		// 其他类型按引用传递
		// 比如下面的Number是自定义的类
		Number b = new Number(5);
		g1(b);
		System.out.println(b.val);
		g2(b);
		System.out.println(b.val);

		// 比如下面的一维数组
		int[] c = { 1, 2, 3, 4 };
		g3(c);
		System.out.println(c[0]);
		g4(c);
		System.out.println(c[0]);
	}

	public static void f(int a) {
		a = 0;
	}

	public static class Number {
		public int val;

		public Number(int v) {
			val = v;
		}
	}

	public static void g1(Number b) {
		b = null;
	}

	public static void g2(Number b) {
		b.val = 6;
	}

	public static void g3(int[] c) {
		c = null;
	}

	public static void g4(int[] c) {
		c[0] = 100;
	}

	// 单链表节点
	public static class ListNode {
		public int val;
		public ListNode next;

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

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

	// 反转单链表测试链接 : https://leetcode.cn/problems/reverse-linked-list/
	class Solution {

		public static ListNode reverseList(ListNode head) {
			ListNode pre = null;
			ListNode next = null;
			while (head != null) {
				next = head.next;   // 先保存下一个节点
				head.next = pre;    // 当前节点的 next 指针反向
				pre = head;         // pre 前移
				head = next;        // head 前移
			}
			return pre;
		}

	}

	// 双链表节点
	public static class DoubleListNode {
		public int value;
		public DoubleListNode last;
		public DoubleListNode next;

		public DoubleListNode(int v) {
			value = v;
		}
	}

	// 反转双链表
	// 没有找到测试链接
	// 如下方法是对的
	public static DoubleListNode reverseDoubleList(DoubleListNode head) {
	    DoubleListNode pre = null;
	    DoubleListNode next = null;
	    
	    while (head != null) {
	        next = head.next;       // 保存下一节点
	        head.next = pre;        // 反转 next 指针
	        head.last = next;       // 反转 prev 指针
	        pre = head;             // pre 前移
	        head = next;            // head 前移（遍历）
	    }
	    
	    return pre;  // 新的头节点
	}


}

单双链表及其反转-堆栈诠释