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countLeaves

Language/Type: Java binary trees

Write a method named countLeaves that returns the total number of leaf nodes in a binary tree. Your method accepts as its parameter a TreeNode that refers to the root of the tree. For example, the following tree has four leaves (nodes 1, 4, 8, and 9): 

(5 (3 (2 (1)) (4)) (6 / (7 (8) (9))))

Assume that you are interacting with TreeNodes as defined below: 

public class TreeNode {
    public int data;
    public TreeNode left;
    public TreeNode right;
    
    public TreeNode() { ... }
    public TreeNode(int data) { ... }
    public TreeNode(int data, TreeNode left, TreeNode right) { ... }
}
Method: Write a Java method as described, not a complete program or class.

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