常见的链表问题（java）

定义链表结构

1、 单链表

public static class Node{
	public int value;
	public Node next;
	
	public Node(int data){
		value = data;
	}
}

2、双链表

public static class DoubleNode{
		public int value;
		public DoubleNode last;
		public DoubleNode next;
		public DoubleNode(int data) {
			value = data;
		}
	}

打印链表的值

1、单链表

public static void printLinedList(Node head){
	System.out.print("Linked List:");
	while(head != null){
		System.out.print(head.value + " ");
		head = head.next;
	}
	System.out.println();
}

2、双链表

public static void printDoubleLinkedList(DoubleNode head) {
		System.out.print("Double Linked List:");
		DoubleNode end = null;
		while(head != null) {
			System.out.print(head.value + " ");
			end = head;
			head = head.next;
		}
		System.out.print("|");
		
		while(end != null) {
			System.out.print(end.value + " ");
			end = end.last;
		}
		System.out.println();
	}

反转单向链表（重要)

public static Node reverseList(Node head) {
		Node pre = null;
		Node next = null;
		while(head != null) {
			//记录当前节点的下一个节点
			next = head.next;
			//当前节点指向pre
			head.next = pre;
			//pre和head向前进一位
			pre = head;
			head = next;
		}
		return pre;
	}

反转双链表

public static DoubleNode reverseList(DoubleNode head) {
		DoubleNode pre = null;
		DoubleNode next = null;
		while(head != null) {
			next = head.next;
			head.next = pre;
			head.last = next;
			pre = head;
			head = next;
		}
		return pre;
	}

判断单链表是否有环，并且返回入环的第一个节点

 public ListNode detectCycle(ListNode head) {
        if(head == null || head.next == null) return null;
        ListNode slow = head, fast = head, start = head;

        while(fast != null && fast.next != null){
            slow = slow.next;
            fast = fast.next.next;
            if(slow == fast){
                while(slow != start){
                    slow = slow.next;
                    start = start.next;
                }
                return start;
            }
        }
        return null;
        
    }

相交链表

在这里插入代码片