重建二叉树

已知前序和中序遍历顺序构建二叉树的代码如下：

BinaryTreeNode *Construct(int *preorder, int *inorder, int length)
{
if (preorder == NULL || inorder == NULL || length <= 0)
return NULL;
return ConstructCore(preorder, preorder + length - 1, inorder, inorder + length - 1);
}
BinaryTreeNode *ConstructCore(int *startPreorder, int *endPreorder, int *startInorder, int *endInorder)
{
int rootValue = startPreorder[0];
BinaryTreeNode *root = new BinaryTreeNode();
root->value = rootValue;
root->lchild = root->rchild = NULL;
if (startPreorder == endPreorder)
{
if (startInorder == endInorder && *startPreorder == *startInorder)
return root;
else
throw std::exception("Invalid input.");
}
int *rootInorder = startInorder;
while (rootInorder <= endInorder && *rootInorder != rootValue)
++rootInorder;
if (rootInorder == endInorder && *rootInorder != rootValue)
throw std::exception("Invalid input.");

int lefLength = rootInorder - startInorder;
int *leftPreOrderEnd = startPreorder + lefLength;
if (lefLength > 0)
root->lchild = ConstructCore(startPreorder + 1, leftPreOrderEnd, startInorder, rootInorder - 1);
if (lefLength < endPreorder - startPreorder)
root->rchild = ConstructCore(leftPreOrderEnd + 1, endPreorder, rootInorder + 1, endInorder);
return root;
}