1. 题目

2. 思路

(1) 中序遍历+递归

• 给定数组的区间，每次取中间元素创建新的结点，并递归设置左右子树，注意递归前先判断区间是否大于等于1。

3. 代码

public class Test {
    
    
    public static void main(String[] args) {
    
    
        Solution solution = new Solution();
        solution.sortedArrayToBST(new int[]{
    
    -10, -3, 0, 5, 9});
    }
}

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

    private TreeNode sortedArrayToBST(int[] nums, int left, int right) {
    
    
        int mid = left + ((right - left) >>> 1);
        TreeNode node = new TreeNode(nums[mid]);
        if (mid > left) {
    
    
            node.left = sortedArrayToBST(nums, left, mid - 1);
        }
        if (mid < right) {
    
    
            node.right = sortedArrayToBST(nums, mid + 1, right);
        }
        return node;
    }
}