I'm having some difficulty understanding the rules for valid red-black tree. If my understanding is correct there are 4 rules that a tree has to follow to be a red-black tree.
- Every node has a color either red or black.
- Root of tree is always black.
- There are no two adjacent red nodes (A red node cannot have a red parent or red child).
- Every path from root to a NULL node has same number of black nodes.
So I drew the tree below in a quiz, and apparently it's not valid. Could someone tell me why this tree is invalid?
Thank you!