# 29. 删除排序链表中的重复元素

java

```java
// 链表工具类
public class LinkedUtils {
    public static ListNode arrayToLinkedList(int[] array){
        if(array==null) return null;
        //head node 
        ListNode root=new ListNode(-1);
        ListNode p=root;

        int size=array.length;
        int i=0;
        while(i<size){
            ListNode q=new ListNode(array[i++]);
            q.next=null;
            p.next=q;
            p=q;
        }

        return root.next;
    }

    public static void print(ListNode root) {
        if(root==null) System.out.println("root is null");
        else{
            while(root!=null){
                System.out.print(root.val);
                if(root.next!=null){
                    System.out.print("->");
                }
                root=root.next;
            }
            System.out.println();
        }
    }

    public static int length(ListNode root) {
        if(root==null) return 0;
        int n=0;
        while(root!=null){
            root=root.next;
            n++;
        }
        return n;
    }

    // 返回指向链表尾部的指针
    public static ListNode moveToTail(ListNode root) {
        if(root==null) return null;
        ListNode tail=root;
        while(tail.next!=null){
            tail=tail.next;
        }
        return tail;
    }
}


// 定义链表
public class ListNode {
    public int val;
    public ListNode next;

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


/**
 * 83. 删除排序链表中的重复元素.
 * 给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。
 *
 * 示例 1:
 * 输入: 1->1->2
 * 输出: 1->2
 *
 * 示例 2:
 * 输入: 1->1->2->3->3
 * 输出: 1->2->3
 */
public class Solution83 {
    /**
     * 从第二个元素开始，和它之前的元素比较，
     * 如果相同，删除当前节点，继续比较直至末尾
     * @param head
     * @return
     */
    public ListNode deleteDuplicates(ListNode head) {
        ListNode p=head,q=null;
        while(p!=null){
            if(q!=null&&p.val==q.val) {
                q.next=p.next;
                p=q.next;
            }else{
                q=p;
                p=p.next;
            }
        }

        return head;
    }

    public static void main(String[] args) {
        int[] array={
                1,1,2,2,2,2,2
        };
        ListNode head=LinkedUtils.arrayToLinkedList(array);
        ListNode r=new Solution83().deleteDuplicates(head);
        LinkedUtils.print(r);
    }
}
```

python

```
```


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