The height of a binary tree is the number of edges in the longest path from the root
to a leaf in the tree. The maximum possible height of a full binary tree with
23 nodes is _________. (answer in integer)

A quicker route: for a full binary tree, if there are \(I\) internal nodes, there are always \(I+1\) leaves, so total nodes \(N = 2I+1\), which means \(I = (N-1)/2\).
For \(N = 23\): \(I = (23-1)/2 = 11\) internal nodes and \(12\) leaves.
Now think about how tall this tree can get. Height is maximized when the tree is stretched into one long chain instead of being built wide and bushy. Picture a spine of internal nodes going straight down, where each spine node peels off exactly one leaf to the side, except the very last spine node, which ends in two leaves because it still needs 2 children to remain a full node and there is no more spine to continue.
With 11 internal nodes forming this spine, the last spine node sits at depth 10, and its two leaf children sit at depth 11. So the longest path from root to leaf has 11 edges, i.e. height 11. Since every internal node is used purely to extend the chain by one more level, this is the tallest arrangement possible with 11 internal nodes.
Hence the maximum possible height is \(11\).