public static Node BstFrmPostOrder(int[] postorder)
{
PostOrderIndex postOrderIndex = new PostOrderIndex();
postOrderIndex.Index = postorder.Length - 1;
return(BstFrmPostorder(postorder, Int32.MinValue, Int32.MaxValue, postOrderIndex));
}
public static Node BuildTree(int[] postorder, int[] inorder)
{
PostOrderIndex postOrderIndex = new PostOrderIndex();
Dictionary <int, int> inorderDict = new Dictionary <int, int>();
for (int i = 0; i < inorder.Length; i++)
{
inorderDict.Add(inorder[i], i);
}
postOrderIndex.Index = postorder.Length - 1;
return(BuildTreeHelper(postorder, 0, postorder.Length - 1, postOrderIndex, inorderDict));
}
public static Node BuildTreeHelper(int[] postorder, int start, int end, PostOrderIndex postOrderIndex, Dictionary <int, int> inorderDict)
{
if (start > end)
{
return(null);
}
Node root = new Node(postorder[postOrderIndex.Index--]);
int inorderIndex = inorderDict[root.Data];
root.Right = BuildTreeHelper(postorder, inorderIndex + 1, end, postOrderIndex, inorderDict);
root.Left = BuildTreeHelper(postorder, start, inorderIndex - 1, postOrderIndex, inorderDict);
return(root);
}
public static Node BstFrmPostorder(int[] postorder, int min, int max, PostOrderIndex postOrderIndex)
{
if (postOrderIndex.Index < 0)
{
return(null);
}
if (postorder[postOrderIndex.Index] < min || postorder[postOrderIndex.Index] > max)
{
return(null);
}
// -- instead of ++
Node root = new Node(postorder[postOrderIndex.Index--]);
//right before left
root.Right = BstFrmPostorder(postorder, root.Data, max, postOrderIndex);
root.Left = BstFrmPostorder(postorder, min, root.Data, postOrderIndex);
return(root);
}