【LeetCode】Insertion Sort List

题目

Sort a linked list using insertion sort.

解答

链表无法像数组那样从后往前依次比较插入，只能从前往后；在链表首部添加一个哨兵可以稍微简化下代码，代码如下：

/**
 * 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) {
        ListNode ret = new ListNode(-1);
        ListNode cur = head;
        ListNode pre = ret;  

        while(cur!=null){
            ListNode tmp = cur;
            cur=cur.next;
            if(pre.next==null){
                pre.next=tmp;
                tmp.next=null;
                pre=ret;
            }else {
                while(pre.next!=null&&pre.next.val<tmp.val){
                    pre=pre.next;
                }
                tmp.next=pre.next;
                pre.next=tmp;
                pre=ret;
            }
        }
        return ret.next;
    }
}

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