在java中从ArrayList构建平衡的二进制搜索树

import java.util.ArrayList;

public class BalancedBinarySearchTree {
    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int val) {
            this.val = val;
        }
    }

    public static TreeNode sortedArrayToBST(ArrayList<Integer> nums) {
        if (nums == null || nums.size() == 0) {
            return null;
        }

        return buildBST(nums, 0, nums.size() - 1);
    }

    private static TreeNode buildBST(ArrayList<Integer> nums, int start, int end) {
        if (start > end) {
            return null;
        }

        int mid = (start + end) / 2;
        TreeNode root = new TreeNode(nums.get(mid));
        root.left = buildBST(nums, start, mid - 1);
        root.right = buildBST(nums, mid + 1, end);

        return root;
    }

    public static void main(String[] args) {
        ArrayList<Integer> nums = new ArrayList<>();
        nums.add(1);
        nums.add(2);
        nums.add(3);
        nums.add(4);
        nums.add(5);

        TreeNode root = sortedArrayToBST(nums);
        // 遍历打印二叉树
        inorderTraversal(root);
    }

    private static void inorderTraversal(TreeNode root) {
        if (root == null) {
            return;
        }

        inorderTraversal(root.left);
        System.out.print(root.val + " ");
        inorderTraversal(root.right);
    }
}