import java.util.*;
public class Solution {
public ListNode deleteDuplicates (ListNode head) {
if(head==null||head.next==null)
return head;
ListNode p = head;
ListNode q = head.next;
while(q!=null){
if(p.val!=q.val){
p = p.next;
q = q.next;
}else{
while(q!=null && p.val==q.val) q = q.next;
p.next = q;
p = p.next;
}
}
return head;
}
}
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