从预订和按顺序构建二叉树

Question

我正在通过一种方法从给定的预订和顺序数组构建二叉树，但我无法理解下面的步骤

                 preorder_start + offset - inorder_start
                 preorder_start + offset - inorder_start + 1

在方法setLeft()和setRight()中作为参数传递。如果有人能用一个例子来解释我，那将是一个很好的帮助。

public BinaryTreeNode buildTreeFromInorderAndPreOrder(int[] preorder, int preorder_start, int preorder_end,
            int[] inorder, int inorder_start, int inorder_end) {
        if (preorder_start > preorder_end || inorder_start > inorder_end)
            return null;
        int data = preorder[preorder_start];                   //We took the starting root data
        BinaryTreeNode node = new BinaryTreeNode(data);        //created a node containing data 
        int offset = inorder_start;                            //offset to point the index of data in inorder array
        while (offset < inorder_end) {                          //while data is not matched in inorder array
            if (inorder[offset] == data)                     
                break;                                         //we get the offset 
            offset++;                                           
        }
        node.setLeft(buildTreeFromInorderAndPreOrder(preorder, preorder_start + 1,
                preorder_start + offset - inorder_start, inorder, inorder_start, offset - 1));
        node.setRight(buildTreeFromInorderAndPreOrder(preorder, preorder_start + offset - inorder_start + 1,
                preorder_end, inorder, offset + 1, inorder_end));
        return node;                                           //finally return the node
    }