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/**

* Sort a linked list using insertion sort.

*/

/**

* Definition for singly-linked list.

* public class ListNode {

* int val;

* ListNode next;

* ListNode(int x) { val = x; }

* }

*/

public class InsertionSortList147 {

public ListNode insertionSortList(ListNode head) {

if (head == null || head.next == null) return head;

ListNode dummy = new ListNode(0);

ListNode end = new ListNode(head.val);

dummy.next = end;

ListNode p = head.next;

while (p != null) {

ListNode n = new ListNode(p.val);

if (n.val >= end.val) {

end.next = n;

end = n;

} else {

insert(dummy, n);

}

p = p.next;

}

return dummy.next;

}

private void insert(ListNode dummy, ListNode newNode) {

ListNode pre = dummy;

ListNode now = dummy.next;

while (now != null) {

if (now.val >= newNode.val) {

pre.next = newNode;

newNode.next = now;

return;

}

now = now.next;

pre = pre.next;

}

}

/**

* https://discuss.leetcode.com/topic/8570/an-easy-and-clear-way-to-sort-o-1-space

*/

public ListNode insertionSortList2(ListNode head) {

if( head == null ){

return head;

}

ListNode helper = new ListNode(0); //new starter of the sorted list

ListNode cur = head; //the node will be inserted

ListNode pre = helper; //insert node between pre and pre.next

ListNode next = null; //the next node will be inserted

//not the end of input list

while( cur != null ){

next = cur.next;

//find the right place to insert

while( pre.next != null && pre.next.val < cur.val ){

pre = pre.next;

}

//insert between pre and pre.next

cur.next = pre.next;

pre.next = cur;

pre = helper;

cur = next;

}

return helper.next;

}

}