[LeetCode] 147. Insertion Sort List

https://leetcode.com/problems/insertion-sort-list/

思路：从旧链表中取出来，插入新链表中。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode insertionSortList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode dummy = new ListNode(Integer.MIN_VALUE);
        while (head != null) {
            ListNode current = head;
            head = head.next;
            
            ListNode pre = dummy;
            ListNode p = dummy.next;
            while (p != null && p.val < current.val) {
                p = p.next;
                pre = pre.next;
            }
            ListNode tmp = pre.next;
            pre.next = current;
            current.next = tmp;
        }
        return dummy.next;
    }
}