【LeetCode-109】Convert Sorted List to Binary Search Tree

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */class ListNode {int val;ListNode next;ListNode(int x) {val = x;}}class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int x) {val = x;}}public class ConvertSortedListtoBinarySearchTree {ListNode tempHead;public TreeNode sortedListToBST(ListNode head) {if (head == null) {return null;}int length = getLength(head);tempHead = head;TreeNode res = buildTree(0, length - 1);return res;}public TreeNode buildTree(int begin, int end) {if (begin > end) {return null;}int mid = begin + (end - begin) / 2;TreeNode left = buildTree(begin, mid - 1);TreeNode root = new TreeNode(tempHead.val);tempHead = tempHead.next;TreeNode right = buildTree(mid + 1, end);root.left = left;root.right = right;return root;}public int getLength(ListNode head) {int length = 0;while (head != null) {length++;head = head.next;}return length;}}