147.对链表进行插入排序

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode insertionSortList(ListNode head) {
        if(head == null){
            return null;
        }
        ListNode dumyNode = new ListNode(0);
        dumyNode.next = head;
        //记录已经完成排序的结点末尾
        ListNode lastSorted = head;
        //当前需要更新插入的结点
        ListNode current = head.next;
        while(current!=null){
            if(lastSorted.val <= current.val){
                //新插入的值正好是最大值
                lastSorted = lastSorted.next;
            }else{
                //从头开始寻找插入的位置
                ListNode pre = dumyNode;
                while(pre.next.val <= current.val){
                    pre = pre.next;
                }
                //将新结点插入到链表
                lastSorted.next = current.next;
                current.next = pre.next;
                pre.next = current;
            }
            //更新新结点
            current = lastSorted.next;
        }
        return dumyNode.next;
    }
}