leetcode 1008. Construct Binary Search Tree from Preorder Traversal | 1008. 前序遍历构造二叉搜索树（Java）

https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal/

好题。

我知道需要用到 BST 的性质，但是没想出来优雅的方法，看了答案。

class Solution {
    public TreeNode bstFromPreorder(int[] preorder) {
        return buildTree(preorder, Integer.MAX_VALUE);
    }

    int i = 0;

    public TreeNode buildTree(int[] preOrder, int bound) {
        if (i == preOrder.length || preOrder[i] > bound) return null;
        
        TreeNode node = new TreeNode(preOrder[i++]);
        node.left = buildTree(preOrder, node.val);
        node.right = buildTree(preOrder, bound);
        return node;
    }
}