1class Solution {2    private int cursor;3    private final Map<Integer, Integer> index = new HashMap<>();4    public TreeNode buildTree(int[] preorder, int[] inorder) {5        cursor = 0;6        index.clear();7        for (int i = 0; i < inorder.length; i++) index.put(inorder[i], i);8        return build(preorder, 0, inorder.length - 1);9    }10    private TreeNode build(int[] preorder, int left, int right) {11        if (left > right) return null;12        int value = preorder[cursor++];13        TreeNode root = new TreeNode(value);14        int mid = index.get(value);15        root.left = build(preorder, left, mid - 1);16        root.right = build(preorder, mid + 1, right);17        return root;18    }19}