面试题7:重建二叉树

题目描述

输入二叉树前序遍历和中序遍历，重建二叉树

先序找根节点，中序固定位置;递归

BinaryTreeNode *Construct(int *preorder, int *inorder, int length)
{
	if(preorder ==nullptr || inorder == nullptr || length<=0)
	{
		return nullptr;
	}
	return ConstructCore(preorder, preorder + length-1, inorder, inorder +length -1);
	
}

BinaryTreeNode(int *startpreorder, int *endpreorder, int *startinorder, int *endorder)
{
	int rootValue = startpreorder[0];
	BinaryTreeNode *root = new BinaryTreeNode();
	root->m_nValue = rootValue;
	root->m_pLeft = root->m_pRight = nullptr;
	if(startpreorder == endpreorder)
	{
		if(startinorder == endinorder && *startpreorder == *startinorder)
		{
			return nullptr;
		}
		else throw std::exception("Invalid input");
	}
	int *rootInorder = startinorder;
	while(rootInorder <= endinorder && *rootInorder != rootValue)
	{
		++rootInorder;
	}
	if(rootInorder == endInorder && *rootInder != rootValue)
	{
		throw std::exception("Invalid");
	}
	int leftLength = rootInorder - startinorder;
	int *leftPreorderEnd = startinorder + leftLength;
	if(leftLength>0)
	{
		root->m_pLeft = ConstructCore(startpreorder + 1, leftPreorderEnd, startinorder, rootInorder-1)
	}
	if(leftLength <endpreorder - startpreorder)
	{
		root->m_pRight = ConstructCore(startpreorder+leftLength+1, endinorder, endPreorder, rootInorder+1, endinorder);
	}
	return root;
	}

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