147. Insertion Sort List

Sort a linked list using insertion sort.

A graphical example of insertion sort. The partial sorted list (black) initially contains only the first element in the list.
With each iteration one element (red) is removed from the input data and inserted in-place into the sorted list

Algorithm of Insertion Sort:

1.Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list.
2.At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there.
3.It repeats until no input elements remain.

Example 1:

Input: 4->2->1->3
Output: 1->2->3->4

Example 2:

Input: -1->5->3->4->0
Output: -1->0->3->4->5

难度：medium

题目：用直插法实现链表排序。

思路：插入排序。

Runtime: 28 ms, faster than 56.45% of Java online submissions for Insertion Sort List.
Memory Usage: 39.9 MB, less than 100.00% of Java online submissions for Insertion Sort List.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode insertionSortList(ListNode head) {
        if (null == head) {
            return head;
        }
        
        ListNode dummyHead = new ListNode(0);
        while (head != null) {
            ListNode tNode = head;
            head = head.next;
            tNode.next = null;
            ListNode nHead = dummyHead;
            while (nHead.next != null && tNode.val > nHead.next.val) {
                nHead = nHead.next;
            }
            tNode.next = nHead.next;
            nHead.next = tNode;
        }
        
        return dummyHead.next;
    }
}