題目連結：108. 將有序陣列轉換為二叉搜尋樹 - 力扣（LeetCode） (leetcode-cn.com)

該問題的核心是弄清楚搜尋樹中序遍歷得到的是一個有序的陣列，所以從有序陣列出發我們需要構建一棵二叉搜尋樹，又要保持平衡，因為選擇中間數字作為根結點，根結點兩邊的樹對應著陣列中間位置左右兩邊的陣列，依次遞迴來構建樹便可以。

/**
 * 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 {

  

//        @Override
//        public String toString() {
//            return "TreeNode{" +
//                    "val=" + val +
//                    ", left=" + left +
//                    ", right=" + right +
//                    '}';
//        }
    // }

    public TreeNode sortedArrayToBST(int
 
[] nums) {
        return dfs(nums,0,nums.length-1);
    }

    private TreeNode dfs(int[] nums, int left, int right) {
        if (left > right) return null;
        int mid = (left + right) / 2;
        TreeNode treeNode = new TreeNode(nums[mid]);
        treeNode.left = dfs(nums,left,mid-1);
        treeNode.right 
 
= dfs(nums,mid+1,right);
        return treeNode;
}}