TreeNode* buildTreeCore(vector<int>& preorder,int prestart,int prend,vector<int>& inorder,int instart,int inend)
{
if(prestart>prend)
return NULL;
int key=preorder[prestart];
TreeNode *root=new TreeNode(key);
int pos=0;
for(int i=instart;i<=inend;i++)
if(inorder[i]==key)
{
pos=i;
break;
}
int leftlen=pos-instart,rightlen=inend-pos;
(*root).left=buildTreeCore(preorder,prestart+1,prestart+leftlen,inorder,instart,pos-1);
(*root).right=buildTreeCore(preorder,prestart+leftlen+1,prend,inorder,pos+1,inend);
return root;
}
void buildTreeCore(TreeNode *root, vector<int> &inorder, int inBegin, int inEnd, vector<int> &postorder, int postEnd) {
if (postEnd < 0)
return;
root->val = postorder[postEnd];
int inPartition = find(inorder, inBegin, inEnd, root->val);
if (inPartition >= 0) {
if (inBegin < inPartition) {
root->left = new TreeNode(0);
buildTreeCore(root->left, inorder, inBegin, inPartition - 1, postorder, postEnd - (inEnd - inPartition) - 1);
}
if (inPartition < inEnd) {
root->right = new TreeNode(0);
buildTreeCore(root->right, inorder, inPartition + 1, inEnd, postorder, postEnd - 1);
}
}
}
TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
if (inorder.empty() || postorder.empty())
return NULL;
if (inorder.size() != postorder.size())
throw "The length of inorder and postorder sequences must be the same.";
TreeNode *root = new TreeNode(0);
buildTreeCore(root, inorder, 0, inorder.size() - 1, postorder, postorder.size() - 1);
return root;
}
TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder)
{
if(preorder.empty())
return NULL;
return buildTreeCore(preorder,0,preorder.size()-1,inorder,0,inorder.size()-1);
}
