LeetCode#109. Convert Sorted List to Binary Search Tree

• 题目：将一个排序后链表转成一个平衡二叉查找树

• 难度：Medium

• 思路：这题的思路跟将有序数组转成平衡二叉查找树一样，查找一个链表的中间元素需要定义两个指针，fast指针每次移动两步，slow指针每次移动一步，fast指针移动到链表尾部时，slow指向的节点为中间节点

• 代码：

public class Solution {    public TreeNode sortedListToBST(ListNode head) {        if(head == null){            return null;        }        return recursion(head, null);    }     public TreeNode recursion(ListNode head, ListNode tail){        if(head == tail){            return null;        }        ListNode slow = head;        ListNode fast = head;        while(fast != tail && fast.next != tail){            slow = slow.next;            fast = fast.next.next;        }        TreeNode node = new TreeNode(slow.val);        node.left = recursion(head, slow);        node.right = recursion(slow.next, tail);        return node;    }}