Description

Sort a linked list using insertion sort.

Example

Given1->3->2->0->null, return0->1->2->3->null.

Solution

注意把cur node插到前面去以后，把之前的cur.prev指到cur.next

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param head: The first node of linked list.
     * @return: The head of linked list.
     */
    public ListNode insertionSortList(ListNode head) {
        // write your code here
        if (head == null) {
            return head;
        }

        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode prev = dummy.next;
        ListNode cur = dummy.next.next;
        while (cur != null) {
            ListNode next = cur.next;
            if (prev.val > cur.val) {
                insert(dummy, cur);
            } else {
                prev = cur;
            }

            prev.next = next;
            cur = next;
        }

        return dummy.next;
    }

    private void insert(ListNode dummy, ListNode cur) {
        ListNode prev = dummy;
        while (prev.next != null && prev.next.val <= cur.val) {
            prev = prev.next;
        }

        ListNode next = prev.next;
        prev.next = cur;
        cur.next = next;
    }
}