【LeetCode】【147】【Insertion Sort List】【链表】

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题目：Sort a linked list using insertion sort.
解题思路：链表的插入排序，基本原理跟顺序表一样的，仔细理解就好。dummyNode是真的好用
代码：

  class ListNode {
      int val;
      ListNode next;
      ListNode(int x) { val = x; }
  }
    public ListNode insertionSortList(ListNode head) {
        if(head == null) return head;
        ListNode dummyNode  = new ListNode(Integer.MIN_VALUE);
        dummyNode.next = new ListNode(head.val);
        ListNode pre = dummyNode;
        ListNode p = dummyNode.next;
        p.next = null;
        ListNode cur = head.next;
        while (cur!=null){
            ListNode next = cur.next;
            while (p!=null && p.val < cur.val){
                pre = p;
                p = p.next;
            }
            pre.next = cur;
            cur.next = p;

            pre = dummyNode;
            p = dummyNode.next;
            cur = next;

        }
        return dummyNode.next;
    }