［LeetCode］Convert Sorted List to Binary Search Tree

解题思路：

1，中叙遍历

2，记录list的长度

public class Solution {    private ListNode list;        public TreeNode sortedListToBST(ListNode head) {                int num = 0;        ListNode p = head;        while(p != null){            p = p.next;            num += 1;        }        list = head;                return sortedListToBST(0, num-1);    }        private TreeNode sortedListToBST(int start, int end){        if (start > end) return null;        int mid = (start + end) / 2;        TreeNode leftTree = sortedListToBST(start, mid-1);        TreeNode node = new TreeNode(list.val);        node.left = leftTree;        list = list.next;        node.right = sortedListToBST(mid+1, end);                return node;    }}