Chapter 18, Problem 11PE

Program Plan Intro

Generic Permutation Generator

Program plan:

Filename: “PermutationGenerator.java”

This code snippet creates a class “PermutationGenerator”. In the code,

• Import the required packages.
• Define a generic class “PermutationGenerator”.
  • Declare a “List” named “list”.
  • Define the constructor “PermutationGenerator ()”.
    • Set the “list”.
  • Define the method “getPermutations()”.
    • Create an array list “result”.
    • If “list.size()” is equal to zero,
      • Add “list” to result.
      • Return “result”.
        • Iterate “for” loop,
        • • Create an array list named “shorterList” of type “List<E>”.
          • Remove an element “i” from “shorterList”.
          • Generate permutations of “shorterList” and save to “shorterPermutationGenerator”.
          • Create an array list “shorterListPermutations”.
          • Iterate a “for” loop,
            • Create an array list named “lst” of type “List<E>”.
            • Add element “i” of “list” to “lst”.
            • Add elements “l” to “lst”.
            • Add “lst” to “result”.
        • Return “result”.

Filename: “PermutationTester.java”

This code snippet creates a class “PermutationTester”. In the code,

• Import the required packages.
• Define a class “PermutationTester”.
  • Define the “main” method.
  • Define a “ArrayList” named “list”.
  • Add elements to “list” using the method “add()”.
  • Create an object “generator” of “PermutationGenerator”.
  • Define another array list “permutations” to store the permutations of “list”.
  • Print the first permutation from array list “permutations”.
  • Print the expected result.
  • Print the second permutation from array list “permutations”.
  • Print the expected result.
  • Print the third permutation from array list “permutations”.
  • Print the expected result.
  • Print the size of “permutations”.
  • Print the expected size.