The given code in main.cpp reads and parses input, and builds the tree for you. Nodes are presented in the form $($key$,$ leftChild, rightChild$),$ where leftChild and rightChild can be nested nodes or "None". A leaf node is of the form $($key$).$ After parsing tree input, the BSTChecker::CheckBSTValidity$()$ function is called and the returned node's key, or $"$No violation", is printed.

X is in the right subtree of ancestor Y$,$ but X$\text{'}$s key is $<$ Y$\text{'}$s key

X$\text{'}$s left or right child points to an ancestor