class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        if (postorder.length == 0) return null;
        int rootVal = postorder[postorder.length - 1];
        int p = indexOf(inorder, rootVal);
        int[] leftInorder = Arrays.copyOfRange(inorder, 0, p);
        int[] rightInorder = Arrays.copyOfRange(inorder, p + 1, inorder.length);
        int[] leftPreorder = Arrays.copyOfRange(postorder, 0, p);
        int[] rightPreorder = Arrays.copyOfRange(postorder, p, postorder.length - 1);

        TreeNode root = new TreeNode(rootVal);
        root.left = buildTree(leftInorder, leftPreorder);
        root.right = buildTree(rightInorder, rightPreorder);
        return root;
    }

    int indexOf(int[] arr, int target) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == target) return i;
        }
        return -1;
    }
}