LeetCode - Construct Binary Tree from Inorder and Postorder Traversal

public TreeNode buildTree(int[] inorder, int[] postorder) {
    return buildTreeHelper(inorder, postorder, 0, postorder.length - 1, postorder.length - 1);
}

public TreeNode buildTreeHelper(int[] inorder, int[] postorder, int start, int end, int index) {
    if(start > end || index < 0)
        return null;
    int rootVal = postorder[index];
    TreeNode root = new TreeNode(rootVal);
    int rootIndex = start;
    for(; rootIndex <= end; rootIndex++)
        if(inorder[rootIndex] == rootVal)
            break;
    root.left = buildTreeHelper(inorder, postorder, start, rootIndex - 1, index + rootIndex - end - 1);
    root.right = buildTreeHelper(inorder, postorder, rootIndex + 1, end, index - 1);
    return root;
}