BinaryTreeNode* ConstructCore
( int* startPreorder, int* endPreorder,
int* startInorder, int* endInorder)
{
// 前序遍历序列的第一个数字是根结点的值
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结点的值
int* rootInorder = startInorder;
while(rootInorder <= endInorder
&& *rootInorder != rootValue)
++ rootInorder;
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;
}
BinaryTreeNode* ConstructCore(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder){
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 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 leftLength = rootInorder-startInorder;
int* leftPreorderEnd = startPreorder+leftLength;
if(leftLength>0){
root->m_pLeft = ConstructCore(startPreorder+1, leftPreorderEnd,startInorder,rootInorder-1);
if(leftLength<endPreorder-startPreorder){
root->m_pRight = ConstructCore(leftPreorderEnd+1, endPreorder,rootInorder+1,endInorder);
}
return root;
}
}
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);
}