LeetCode109-20.8.18-有序链表转二叉搜索树

题目链接：LeetCode109
过程：一开始想直接写二叉搜索树，一个节点一个节点的插入树中，但感觉好麻烦而且不会。索性去看题解。（我太呆了 ）题解真好。
做法：分治，评论里有位bfs建树,dfs中序遍历填值感觉可以。
代码：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */

class Solution {
    ListNode globalNode;
    public TreeNode sortedListToBST(ListNode head) {
        int len=0;
        for(ListNode node=head;node!=null;node=node.next)len++;
        globalNode=head;
        return buildTree(0,len-1);
           
    }
    public TreeNode buildTree(int left,int right){
        if(left>right)return null;
        int mid=(left+right+1)/2;
        TreeNode node=new TreeNode();
        node.left=buildTree(left,mid-1);
        node.val=globalNode.val;
        globalNode=globalNode.next;
        node.right=buildTree(mid+1,right);
        return node;
    }
    
}