Java: Complete the methods marked TODO. Will rate youranswer!

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package search;

import java.util.ArrayList;
import java.util.List;

/**
* An abstraction over the idea of a search.
*
* @author liberato
*
* @param : generic type.
*/
public abstract class Searcher {
protected final SearchProblem searchProblem;
protected final List visited;
protected List solution;

/**
   * Instantiates a searcher.
   *
   * @param searchProblem
  *           the search problem for which this searcher will find and
  *           validate solutions
   */
public Searcher(SearchProblem searchProblem) {
    this.searchProblem = searchProblem;
    this.visited = new ArrayList();
}

/**
   * Finds and return a solution to the problem,consisting of a list of
   * states.
   * The list should start with the initial state of theunderlying problem.
   * Then, it should have one or more additional states.Each state should be
   * a successor of its predecessor. The last stateshould be a goal state of
   * the underlying problem.
   * If there is no solution, then this method shouldreturn an empty list.
   *
   * @return a solution to the problem (or an emptylist)
   */
public abstract List findSolution();

/**
   * Checks that a solution is valid.
   * A valid solution consists of a list of states. Thelist should start with
   * the initial state of the underlying problem. Then,it should have one or
   * more additional states. Each state should be asuccessor of its
   * predecessor. The last state should be a goal stateof the underlying
   * problem.
   *
   * @param solution : solution
   * @return true iff this solution is a validsolution
   * @throws NullPointerException
  *            if solution is null
   */
public final boolean isValidSolution(List solution){
        // TODO
        return false;
}
}

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package search;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Stack;

/**
* An implementation of a Searcher that performs an iterativesearch,
* storing the list of next states in a Stack. This results ina
* depth-first search.
*
*/
public class StackBasedDepthFirstSearcher extendsSearcher {

/**
   * StackBasedDepthFirstSearcher.
   * @param searchProblem : search problem
   */
public StackBasedDepthFirstSearcher(SearchProblemsearchProblem) {
    super(searchProblem);
}

@Override
public List findSolution() {
    // TODO
    return null;
}
}

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package search;

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

/**
* An implementation of a Searcher that performs an iterativesearch,
* storing the list of next states in a Queue. This results ina
* breadth-first search.
*
*/
public class QueueBasedBreadthFirstSearcher extendsSearcher {

/**
   * QueueBasedBreadthFirstSearcher.
   * @param searchProblem : search problem
   */
public QueueBasedBreadthFirstSearcher(SearchProblemsearchProblem) {
    super(searchProblem);
}

@Override
public List findSolution() {
    // TODO
    return null;
}
}

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package mazes;

import java.util.List;

import search.Solver;

public class MazeDriver {

/**
   * Supproting main method.
   */
public static void main(String[] args) {
    MazeGenerator mg = new MazeGenerator(24, 8,0);
    Maze m = mg.generateDFS();
    System.out.println(m.toString());
    Solver s = newSolver(m);
    List r =s.solveWithRecursiveDFS();
    for (Cell cell : r) {
      System.out.println(cell);
    }
    System.out.println(r.size());
    // System.out.println(\"--------\");
    // List d =s.solveWithIterativeDFS();
    // for (Cell cell : d) {
    //   System.out.println(cell);
    // }
    // System.out.println(d.size());
    // System.out.println(\"--------\");
    // List q = s.solveWithBFS();
    // for (Cell cell : q) {
    //   System.out.println(cell);
    // }
    // System.out.println(q.size());
}
}

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package puzzle;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import search.SearchProblem;
import search.Solver;

/**
* A class to represent an instance of the eight-puzzle.
* The spaces in an 8-puzzle are indexed as follows:
* 0 | 1 | 2
* --+---+---
* 3 | 4 | 5
* --+---+---
* 6 | 7 | 8
* The puzzle contains the eight numbers 1-8, and an emptyspace.
* If we represent the empty space as 0, then the puzzle issolved
* when the values in the puzzle are as follows:
* 1 | 2 | 3
* --+---+---
* 4 | 5 | 6
* --+---+---
* 7 | 8 | 0
* That is, when the space at index 0 contains value 1, thespace
* at index 1 contains value 2, and so on.
* From any given state, you can swap the empty space with aspace
* adjacent to it (that is, above, below, left, or right ofit,
* without wrapping around).
* For example, if the empty space is at index 2, you may swap
* it with the value at index 1 or 5, but not any other index.
* Only half of all possible puzzle states are solvable! See:
* https://en.wikipedia.org/wiki/15_puzzle
* for details.
*

* @author liberato
*
*/
public class EightPuzzle implementsSearchProblem> {

/**
   * Creates a new instance of the 8 puzzle with thegiven starting values.
   * The values are indexed as described above, andshould contain exactly the
   * nine integers from 0 to 8.
   *
   * @param startingValues
  *           the starting values, 0 -- 8
   * @throws IllegalArgumentException
  *            if startingValues is invalid
   */
public EightPuzzle(List startingValues) {
}

@Override
public List getInitialState() {
    // TODO
    return null;
}

@Override
public List>getSuccessors(List currentState) {
    // TODO
    return null;
}

@Override
public boolean isGoal(List state) {
    // TODO
    return false;
}

/**
   * supporting man method.
   */
public static void main(String[] args) {
    EightPuzzle e = newEightPuzzle(Arrays.asList(new Integer[] { 1, 2, 3,
        4, 0, 6, 7, 5, 8}));

    List> r = newSolver>(e).solveWithBFS();
    for (List l : r) {
      System.out.println(l);
    }
}
}