public static ListNode sortedMerge(ListNode head1, ListNode head2) {
if (head1 == null) return head2;
if (head2 == null) return head1;
ListNode newHead = new ListNode(-100);
ListNode currentNewHead = newHead;
ListNode currentHead1 = head1;
ListNode currentHead2 = head2;
while (currentHead1 != null && currentHead2 != null) {
if (currentHead1.val < currentHead2.val) {
ListNode ch1Next = currentHead1.next;
currentNewHead = insertAfterNode(currentNewHead, currentHead1);
currentHead1 = ch1Next;
} else {
ListNode ch2next = currentHead2.next;
currentNewHead = insertAfterNode(currentNewHead, currentHead2);
currentHead2 = ch2next;
}
currentNewHead = currentNewHead.next;
}
if (currentHead1 == null) {
currentNewHead.next = currentHead2;
} else {
currentNewHead.next = currentHead1;
}
return newHead.next;
}
public static ListNode[] frontBackSplit(ListNode head) {
ListNode[] firstSecond = new ListNode[2];
if (head == null) return firstSecond;
if (head.next == null) {
firstSecond[0] = head;
return firstSecond;
}
ListNode slowCurrentHeadTrailer = head;
ListNode slowCurrentHead = head;
ListNode fastCurrentHead = head;
while (fastCurrentHead.next != null && fastCurrentHead.next.next != null) {
slowCurrentHeadTrailer = slowCurrentHead;
slowCurrentHead = slowCurrentHead.next;
fastCurrentHead = fastCurrentHead.next.next;
}
if (fastCurrentHead != null) {
slowCurrentHeadTrailer = slowCurrentHead;
slowCurrentHead = slowCurrentHead.next;
}
slowCurrentHeadTrailer.next = null;
firstSecond[0] = head;
firstSecond[1] = slowCurrentHead;
return firstSecond;
}
public static ListNode removeDuplicates2(ListNode head) {
if (head == null) return head;
ListNode current = head;
while (current != null && current.next != null) {
if (current.val == current.next.val) {
current.next = current.next.next;
}
current = current.next;
}
return head;
}
public static ListNode sortedInsert(ListNode head, ListNode newNode) {
if (head == null || head.val > newNode.val) return insertAtHead(head, newNode);
ListNode current = head;
while (current != null && current.next != null) {
if (current.next.val > newNode.val) {
insertAfterNode(current, newNode);
return head;
}
current = current.next;
}
current.next = newNode;
newNode.next = null;
return head;
}
public static ListNode recursiveReverseLinkedList(ListNode head) {
if (head == null || head.next == null) return head;
ListNode newHead = recursiveReverseLinkedList(head.next);
head.next.next = head;
head.next = null;
return newHead;
}
public static ListNode removeDuplicates(ListNode head) {
ListNode newHead = null;
if (head == null) return head;
ListNode current = head.next;
newHead = insertAtHead(newHead, head);
ListNode newCurrent = newHead;
int lastVal = newCurrent.val;
while (current != null) {
ListNode nextNode = current.next;
current.next = null;
if (lastVal != current.val) {
newCurrent = insertAfterNode(newCurrent, current);
newCurrent = newCurrent.next;
lastVal = current.val;
}
current = nextNode;
}
return newHead;
}
public static ListNode[] frontBackSplit2(ListNode head) {
ListNode[] firstSecond = new ListNode[2];
if (head == null) return firstSecond;
if (head.next == null) {
firstSecond[0] = head;
return firstSecond;
}
ListNode slowCurrent = head;
ListNode fastCurrent = head.next;
while (fastCurrent != null && fastCurrent.next != null) {
slowCurrent = slowCurrent.next;
fastCurrent = fastCurrent.next.next;
}
firstSecond[0] = head;
firstSecond[1] = slowCurrent.next;
slowCurrent.next = null;
return firstSecond;
}
public static ListNode insertAfterNode(ListNode currentNode, int value) {
ListNode newNode = new ListNode(value);
newNode.next = currentNode.next;
currentNode.next = newNode;
return currentNode;
}
public static ListNode insertAtHead(ListNode currentNode, ListNode newNode) {
newNode.next = currentNode;
return newNode;
}
public static ListNode insertAtHead(ListNode currentNode, int value) {
ListNode newNode = new ListNode(value);
newNode.next = currentNode;
return newNode;
}
public static ListNode insertAtTail(ListNode currentNode, ListNode newNode) {
currentNode.next = newNode;
newNode.next = null;
return currentNode;
}
public static ListNode insertAfterNode(ListNode currentNode, ListNode newNode) {
newNode.next = currentNode.next;
currentNode.next = newNode;
return currentNode;
}