Introduction to Binary Trees - Advanced Topics in Java: Core Concepts in Data Structures - page 246

private int countLeaves(TreeNode root) {
if (root == null) return 0;
if (root.left == null && root.right == null) return 1;
return countLeaves(root.left) + countLeaves(root.right);
}

And the next returns the height of the tree:

public int height() {
return numLevels(root);
}

private int numLevels(TreeNode root) {
if (root == null) return 0;
return 1 + Math.max(numLevels(root.left), numLevels(root.right));
}

Math.max returns the larger of its two arguments.
You are advised to dry-run these functions on some sample trees to verify that they do return the correct values.

8.11 Binary Search Tree Deletion
Consider the problem of deleting a node from a binary search tree (BST) so that it remains a BST. There are three
cases to consider:

1.

The node is a leaf.

2.

(a) The node has no left subtree.

(b) The node has no right subtree.

3.

The node has non-empty left and right subtrees.

We illustrate these cases using the BST shown in Figure 8-9 .

H

L

F

R

A J

T

N

C

D P

B

Figure 8-9. A binary search tree