203. Remove linked list elements (linked list)

The question ： Delete the given value in the list val All nodes of .

Example 1：
Input ：head = [1,2,6,3,4,5,6], val = 6
Output ：[1,2,3,4,5]

Example 2：
Input ：head = [], val = 1
Output ：[]

Example 3：
Input ：head = [7,7,7,7], val = 7
Output ：[]

Method 1 ： Use sentinel nodes

public class Yichulianbiaoyuansu {
    static class ListNode<E>{
        ListNode next; //  Object references the next node object 
        E val;// data ： Node data 

        ListNode(E val){
            this.val = val;
        }
    }

    public ListNode removeElements(ListNode head,int val){
        // If the header node is empty , Returns an empty 
        if(head==null){
            return null;
        }
        // Defining sentinel nodes 
        ListNode dummy = new ListNode(-1);
        ListNode pre = dummy;
        ListNode cur = head;
        while (cur!=null){
            // If the current node is the node to be deleted 
            if ((int)cur.val==val){
                ListNode node = cur.next;// preservation cur The next node of the current node 
                cur.next = null;// Release the space pointed to by the current node （ stay java This step can be omitted , from JVM Garbage collection handles the release of memory space ）
                pre.next = node;
            }else {
                pre = cur;
            }
            cur = cur.next;
        }
        return dummy.next;
    }

    public static void main(String[] args) {
        ListNode node1 = new ListNode(1);
        ListNode node2 = new ListNode(4);
        ListNode node3 = new ListNode(2);
        ListNode node4 = new ListNode(4);
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;

        Yichulianbiaoyuansu yichulianbiaoyuansu = new Yichulianbiaoyuansu();
        ListNode res =yichulianbiaoyuansu.removeElements(node1,1);
        // Create a linked list node 
        while (res!=null){
            if(res.next==null){
                System.out.print(res.val);
            }else {
                System.out.print(res.val + "->");
            }
            res = res.next;
        }
    }
}