Chapter 21, Problem 7AW

Explanation of Solution

Algorithm to define a comparator class “DecOrder”:

Step 1: Define a static comparator class “DecOrder”.

Step 2: Inside that function declare a method “compare” to compare two strings.

Step 3: Inside the “compare” method, check if the length of string “s” is equal to the length of the string “t”. If it is true, then return “s.compareTo (t)”.

Step 4: If it is not true, then return “s.length () – t.length()”.

Function to count the number of leaf in a binary tree:

//Define the static comparator class

static class DecOrder implements Comparator<String>

{

    //Define a method named "compare"

    public int compare(String s, String t)

    {

//Check if the length of "s" is equal to length of "t"

        if (s.length() == t.length())

//Return the value that results from "compareTo" operation

            return s...