Delete duplicate elements in the sorting linked list ii[unified operation of linked list nodes --dummyhead]

Preface

For the operation of linked list , There are two cores . First of all , Chain cannot be broken , The core of broken chain is not to let passive nodes not be referenced . second , The first node operation / Empty linked list operation , This can be handled uniformly through the header node .

One 、 Delete duplicate elements from the sort list II

Two 、dummyHead Unify the empty linked list and the first node operation

package everyday.doublePoint;

//  Delete duplicate elements from the sort list  II
public class DeleteDuplicates {
    
    /* target： Delete duplicate elements in linked list , The linked list has been sorted , It means just delete and pre Same element .  How to be the same as the following , Just traverse to different positions . */
    public ListNode deleteDuplicates(ListNode head) {
    
        //  Unified header node operation , And the special case node is null The situation of , very nice Of dummy
        ListNode dummyHead = new ListNode();
        ListNode tail = dummyHead;//  Set new linked list tail node .
        while (head != null) {
    
            //  Legal node , String it in the new linked list tail After node .
            if (head.next == null || head.next.val != head.val) {
    
                tail.next = head;
                //  to update head Go to the next step 
                head = head.next;
                //  to update tail
                tail = tail.next;
                tail.next = null;
                continue;
            }
            //  Illegal nodes , Traverse a string 
            while (head.next != null && head.next.val == head.val) head = head.next;
            head = head.next;
        }
        //  Return to the first node .
        return dummyHead.next;
    }

    // Definition for singly-linked list.
    public class ListNode {
    
        int val;
        ListNode next;

        ListNode() {
    
        }

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

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

}

summary

1）dummyHead, Unify the operation of the empty linked list and the first node .

reference

[1] LeetCode Delete duplicate elements from the sort list II