[Leetcode] Sort list (sorting)

This question requires two linked lists to be sorted by merging. The basic idea is to split and merge them.

The Merged Code is clearly described in the merge two sorted list. So the code is provided here.

public ListNode merge(ListNode l1, ListNode l2) {ListNode helper = new ListNode(0);ListNode runner = helper;while (l1 != null && l2 != null) {if (l1.val < l2.val) {runner.next = l1;l1 = l1.next;runner = runner.next;} else {runner.next = l2;l2 = l2.next;runner = runner.next;}if (l1 != null)runner.next = l1;if (l2 != null)runner.next = l2;}return helper.next;}

The idea of separation is very important. In the array, it ends when only one element is left, and the same is true for the chain table.

The method for judging only one element in the array is if (Left = right)

The method for determining only one element in the linked list is if (head. Next = NULL)

The Division Method in the array is

int middle = (left + right) / 2;mergeSort(array, left, middle);mergeSort(array, middle + 1, right);merge(array, left, middle, right);

How can I find the middle in the linked list? At this time, we think of the walker_runner technology mentioned above to find the point.

ListNode walker = head;ListNode runner = head;while (runner.next != null && runner.next.next != null) {walker = walker.next;runner = runner.next.next;}ListNode head2 = walker.next;walker.next = null;head = mergeSort(head);head2 = mergeSort(head2);return merge(head, head2);

The complete code is provided below

public ListNode sortList(ListNode head) {if (head == null)return head;return mergeSort(head);}public ListNode mergeSort(ListNode head) {if (head.next == null)return head;ListNode walker = head;ListNode runner = head;while (runner.next != null && runner.next.next != null) {walker = walker.next;runner = runner.next.next;}ListNode head2 = walker.next;walker.next = null;head = mergeSort(head);head2 = mergeSort(head2);return merge(head, head2);}public ListNode merge(ListNode l1, ListNode l2) {ListNode helper = new ListNode(0);ListNode runner = helper;while (l1 != null && l2 != null) {if (l1.val < l2.val) {runner.next = l1;l1 = l1.next;runner = runner.next;} else {runner.next = l2;l2 = l2.next;runner = runner.next;}if (l1 != null)runner.next = l1;if (l2 != null)runner.next = l2;}return helper.next;}

[Leetcode] Sort list (sorting)