@Test
public void Test1() {
ListNode node11 = new ListNode(1);
ListNode node21 = new ListNode(2);
ListNode actual = solution.mergeTwoLists(node11, node21);
ListNode node1 = new ListNode(1);
ListNode node2 = new ListNode(2);
node1.next = node2;
ListNode expect = node1;
assertTrue(ListNode.isSameList(actual, expect));
}
public ListNode deleteDuplicates(ListNode head) {
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode pre = dummy; // last unique node we found
ListNode node = pre.next;
while (node != null) {
// find the last node that has the same value as current node
while (node.next != null && node.next.val == node.val) {
node = node.next;
}
// now, node has different value from its next node (if next
// node exists), we need to compare with previous node to
// see whether `node` has unique value
if (pre.next == node) {
// ! don't use (pre.val == node.val) unless you are sure
// dummy has different value from head node
pre = node;
} else {
pre.next = node.next;
}
node = node.next;
}
return dummy.next;
}