Leetcode: Insertion Sort List

Sort a linked list using insertion sort.

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode insertionSortList(ListNode head) {        if (head == null || head.next == null) {            return head;        }                ListNode dummy = new ListNode(0);        dummy.next = head;                ListNode pre = head;        ListNode curr = head.next;        while (curr != null) {            ListNode p1 = dummy;            ListNode p2 = dummy.next;            while (p2 != curr) {                if (p2.val > curr.val) {                    pre.next = curr.next;                    p1.next = curr;                    p1.next.next = p2;                    curr = pre.next;                    break;                } else {                    p1 = p2;                    p2 = p1.next;                }            }            if (p2 == curr) {                pre = curr;                curr = pre.next;            }        }                return dummy.next;    }}