重建二叉树

题目描述：
输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并输出它的后序遍历序列。

struct BinaryTreeNode
{
int m_nValue;
BinaryTreeNode* m_pLeft;
BinaryTreeNode* m_pRight;
};

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)
{
//前序遍历序列的第一个数字是根节点的值
int rootValue = startPreorder[0];
BinaryTreeNode* root = new BinaryTreeNode();
root->m_nValue = rootValue;
root->m_pLeft = root->m_pRight = NULL;

if(startPreorder == endPreorder)
{
if(startInorder == endInorder && *startPreorder == *startInorder)
return root;
else
throw std::exception("Invalid input.");
}
//在中序遍历中找到根节点的值
int* rootInorder = startInorder;
while(rootInorder <= endInorder && *rootInorder != rootValue)
++rootInorder;
if(rootInorder == endInorder && *rootInorder != rootValue)
throw std::exception("Invalid input");
int leftLength = rootInorder - startInorder;
int* leftPreorderEnd = startPreorder + leftLength;
if(leftLength > 0)
{
//构建左子树
root->m_pLeft = ConstructCore(startPreorder+1,leftPreorderEnd,startInorder,rootInorder-1);
}
if(leftLength < endPreorder - startPreorder)
{
//构建右子树
root->m_pRight = ConstructCore(leftPreorderEnd+1,endPreorder,rootInorder+1,endInorder);
}
return root;
}