My question is: how can I see the Tuple result in the process method if it was created in the check method? How am I able to use it there, if it was created in a private method?
public class Problem13 {
private Tuple<Integer> costs;
private Tuple<String> names;
private Tuple<Integer> result;
private int budget;
private int minDelta, minCost, totalCost;
public void process(String fileName) {
if (!read(fileName))
return;
if (budget >= totalCost) {
System.out.println("You can buy all items");
return;
}
if (budget < minCost) {
System.out.println("You cannot buy items");
return;
}
minDelta = -1;
int n = costs.getLength();
Set<Integer> interval = new IntegerInterval(0, n - 1);
for (int k = n - 1; k > 0; --k) {
Combinations<Integer> combinations = new Combinations<Integer>(interval, k);
combinations.produce((tuple) -> !check(tuple));
if (minDelta == 0)
break;
}
if (result == null)
System.out.println("No solution found");
else {
int k = result.getLength();
for (int j = 0; j < k; ++j)
System.out.printf("%s ", names.get(result.get(j)));
System.out.printf("(%d)\n", minDelta);
}
}
public static void main(String[] args) {
new Problem13().process("data/input13.txt");
}
private boolean check(Tuple<Integer> tuple) {
int k = tuple.getLength();
int currentCost = 0;
for (int i = 0; i < k; ++i) {
int j = tuple.get(i);
currentCost += costs.get(j);
if (currentCost > budget)
return false;
}
int d = budget - currentCost;
if (minDelta < 0 || d < minDelta) {
minDelta = d;
result = new ArrayTuple<>(k);
for (int i = 0; i < k; ++i)
result.set(i, tuple.get(i));
}
return minDelta == 0;
}
private means private to the class. So Problem13 can see anything defined in that class, whether private, public, protected or package private.
Also, the access modifier of the method only affects who can call it, not where the results can be seen. For instance, if result was defined as a public field, any class (not just Problem13) could see it.
You can find many good breakdowns of access modifiers out there on the Interwebs. Here's one.
For my parallel computing class I have to think and create a parallel implementation of the selection sort algorithm. The idea is to be able to scale it to multiple threads so that it becomes faster than the serial implementation.
My idea was as follows:
Parallel selection sort idea
I have created the following implementation over the last few days but it is much slower than the serial algorithm. Whenever I use more threads it is also much slower vs when I use one thread. This is the first time I am working with threads as well so I am not sure if I implemented that correctly.
SelectionSort.java
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class SelectionSort {
private static final int availableProcessors = Runtime.getRuntime().availableProcessors();
private static final int NUMBER_COUNT = 10000;
private static List<Integer> sortedList = new ArrayList<>();
private static int[][] splitArray;
private static List<Integer> lowestNumbers = new ArrayList<>();
public static void main(String[] args) throws InterruptedException {
List<Integer> numbers = Numbers.GenerateNumber(NUMBER_COUNT);
class Lowest {
synchronized int getLowest(int index) {
int lowestInArray = Integer.MAX_VALUE;
for (int i = 0; i < splitArray[index].length; i++) {
if (splitArray[index][i] < lowestInArray) {
lowestInArray = splitArray[index][i];
}
}
return lowestInArray;
}
}
Lowest lowest = new Lowest();
class SelectionSortThread extends Thread {
private int splitArrayIndex;
private SelectionSortThread(int splitArrayIndex) {
this.splitArrayIndex = splitArrayIndex;
}
public void run() {
lowestNumbers.add(lowest.getLowest(splitArrayIndex));
}
}
long startingTime = System.currentTimeMillis();
for (int i = 0; i < NUMBER_COUNT; i++) {
List<Thread> threads = new ArrayList<>();
splitArray = fillSplitArray(availableProcessors, numbers);
lowestNumbers.clear();
for (int j = 0; j < availableProcessors; j++) {
if(splitArray[j] != null) {
threads.add(new SelectionSortThread(j));
}
}
for (Thread thread : threads) {
thread.start();
}
for (Thread thread : threads) {
thread.join();
}
int lowestInArray = getLowest(lowestNumbers);
numbers = swap(numbers, lowestInArray);
sortedList.add(numbers.get(0));
numbers.remove(0);
}
System.out.println("Sorted list: " + Arrays.toString(sortedList.toArray()));
System.out.println(System.currentTimeMillis() - startingTime);
}
private static int getLowest(List<Integer> lowestNumbers) {
int lowestInArray = Integer.MAX_VALUE;
for (Integer lowestNumber : lowestNumbers) {
if (lowestNumber < lowestInArray) {
lowestInArray = lowestNumber;
}
}
return lowestInArray;
}
private static List<Integer> swap(List<Integer> list, int lowest)
{
int n = list.size();
for(int i = 0; i < n; i++)
{
if(list.get(i) == lowest) {
Collections.swap(list, 0, i);
return list;
}
}
return null;
}
static int[][] fillSplitArray(int arrayAmount, List<Integer> listToUse) {
if (listToUse.size() == 0) {
return new int[0][0];
}
int splitLength = (int) Math.ceil((double) listToUse.size() / (double) arrayAmount);
int[][] splits = new int[arrayAmount][];
int j = 0;
int k = 0;
for (int i = 0; i < listToUse.size(); i++) {
if (k == splitLength) {
k = 0;
j++;
}
if (splits[j] == null) {
int remainingNumbers = listToUse.size() - i;
splits[j] = new int[Math.min(remainingNumbers, splitLength)];
}
splits[j][k++] = listToUse.get(i);
}
return splits;
};
}
Numbers.java
import java.util.ArrayList;
import java.util.List;
class Numbers {
static List<Integer> GenerateNumber(int numberCount) {
List<Integer> temp = new ArrayList<>();
for (int i = numberCount; i > 0; i--) {
temp.add(i);
}
return temp;
}
}
Is there anything I am doing totally wrong or that I could improve? I am expecting the parallel implementation to be faster than the serial one but so far this is not the case. It is currently a lot slower.
I have class Book with three fields - name, author and isbn
I`m trying to insert the fields in ArrayList and to print:
book1, author1, isbn
book2, author2, isbn2
and... to 10
code:
public class InsertBooks {
private static ArrayList<String> booksNames = new ArrayList<>();
private static ArrayList<String> booksAuthors = new ArrayList<>();
private static ArrayList<Integer> booksIsbn = new ArrayList<>();
private static ArrayList<Book> books = new ArrayList<>();
// adding books in ArrayList booksNames
private static void addBooksNames() {
for (int i = 0; i < 10; i++) {
booksNames.add("Book" + i);
}
}
// adding author in ArrayList booksAuthors
private static void addBooksAuthor() {
for (int i = 0; i < 10; i++) {
booksAuthors.add("Author" + i);
}
}
// adding author in ArrayList booksAuthors
private static void addBooksIsbn() {
for (int i = 0; i < 10; i++) {
booksIsbn.add(Integer.valueOf("isbn" + i));
}
}
public static void fillArrayListOfBooks() {
for (int i = 0; i < 10; i++) {
books.add(new Book((addBooksNames(), addBooksAuthor(), addBooksIsbn()));
}
}
}
You want to call all your add* functions first. Then in the loop of fillArrayListOfBooks() use those values.
void fillArrayListOfBooks()
{
addBooksNames();
addBooksAuthor();
addBooksIsbn();
for (int i = 0; i < 10; i++) {
dbooks.add(new Book(booksNames.get(i), booksAuthors.get(i), booksIsbn.get(i)));
}
}
You could easily get rid of those lists (unless you need them later):
void fillArrayListOfBooks()
{
for (int i = 0; i < 10; i++) {
dbooks.add(new Book("Book" + i, "Author" + i, "isbn" + i));
}
}
Would like some advice on how to access items from an ArrayList and pass them to a constructor.
I have this code that generates and stores 2 ArrayLists of Integer and Date:
ArrayList <Date> days = new ArrayList<>();
Integer[] count = {0,0,0,0,0,0}; //Use Integer not int
List<Integer> recordCount = Arrays.asList(count);
for(int x = 0; x < 7; x++) {
days.add(dateUtils.stringToDateWithTime(lastWeek.toString()));
calendar.add(Calendar.DAY_OF_MONTH, 1);
}
for(int x = 0; x < 7; x++) {
for(int y = 0; y < r.size(); y++) {
if (!(days.get(x) == r.get(y).getDate())) {
int oldValue = recordCount.get(x);
int newValue = oldValue + 1;
recordCount.set(x, newValue);
}
}
}
dataModel.setyValueCount(what do i put in here?);
dataModel.setxValueDate();
And where I would like to pass them to is my DataModel class:
public class DataModel {
private long yValueCount;
private Date xValueDate;
private String someStringField;
private String label;
public DataModel() {
}
public DataModel(Date xValueDate, int yValueCount) {
this.xValueDate = xValueDate;
this.yValueCount = yValueCount;
}
public long getyValueCount() {
return yValueCount;
}
public void setyValueCount(long yValueCount) {
this.yValueCount = yValueCount;
}
public Date getxValueDate() {
return xValueDate;
}
public void setxValueDate(Date xValueDate) {
this.xValueDate = xValueDate;
}
}
This data is to be inserted into a chart that will be displayed in the app. Thanks.
for(int x = 0;x<7;x++)
{
for (int y = 0; y < r.size(); y++) {
//create object here
DataModel dataModel=new DataModel();
if (!(days.get(x) == r.get(y).getDate())) {
int oldValue = recordCount.get(x);
int newValue = oldValue + 1;
recordCount.set(x, newValue);
//set here what do you want
dataModel.setyValueCount(long type);
dataModel.setxValueDate(Date type);
//use dataModel object for any other process like persist
//looking for this or any other..........?
}
}
}
My assignment asks me to make a TV show program, where I can input shows, delete, modify and sort them. What I'm stuck on is the sorting part. With the show, it asks for the name, day a new episode premieres, and time. Those are the keys I need to sort it by.
The program prompts the user to input one of those keys, then the program needs to sort (sorting by day will sort alphabetically).
I made a class and used an array. Here is the class:
public class showInfo
{
String name;
String day;
int time;
}
And the method to sort by time in the code:
public static void intSort()
{
int min;
for (int i = 0; i < arr.length; i++)
{
// Assume first element is min
min = i;
for (int j = i+1; j < arr.length; j++)
{
if (arr[j].time < arr[min].time)
{
min = j;
}
}
if (min != i)
{
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < arr.length; i++)
{
System.out.println(arr[i].name + " - " + arr[i].day + " - " + arr[i].time + " hours");
}
}
When I call it and output it in the main, it only shows "TV Shows by Time" and not the list. Why is this?
Also, I need to make ONE method that I will be able to use to sort both the day AND the name (both Strings). How can I do this without using those specific arrays (arr[i].name, arr[i].day) in the method?
Any help would be greatly appreciated! Thanks in advance!
In this part of your code
if (min != i) {
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
You're just changing the time when you should move the whole object instead. To fix it, the code must behave like this:
if (min != i) {
//saving the object reference from arr[i] in a temp variable
showInfo temp = arr[i];
//swapping the elements
arr[i] = arr[min];
arr[min] = temp;
}
I̶t̶ ̶w̶o̶u̶l̶d̶ ̶b̶e̶ ̶b̶e̶t̶t̶e̶r̶ ̶t̶o̶ ̶u̶s̶e̶ ̶ Arrays#sort ̶w̶h̶e̶r̶e̶ ̶y̶o̶u̶ ̶p̶r̶o̶v̶i̶d̶e̶ ̶a̶ ̶c̶u̶s̶t̶o̶m̶ ̶̶C̶o̶m̶p̶a̶r̶a̶t̶o̶r̶̶ ̶o̶f̶ ̶t̶h̶e̶ ̶c̶l̶a̶s̶s̶ ̶b̶e̶i̶n̶g̶ ̶s̶o̶r̶t̶e̶d̶ ̶(̶i̶f̶ ̶y̶o̶u̶ ̶a̶r̶e̶ ̶a̶l̶l̶o̶w̶e̶d̶ ̶t̶o̶ ̶u̶s̶e̶ ̶t̶h̶i̶s̶ ̶a̶p̶p̶r̶o̶a̶c̶h̶)̶.̶ ̶S̶h̶o̶r̶t̶ ̶e̶x̶a̶m̶p̶l̶e̶:̶
showInfo[] showInfoArray = ...
//your array declared and filled with data
//sorting the array
Arrays.sort(showInfoArray, new Comparator<showInfo>() {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
//basic implementation
if (showInfo1.getTime() == showInfo2.getTime()) {
return showInfo1.getName().compareTo(showInfo2.getName());
}
return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
}
});
//showInfoArray will be sorted...
Since you have to use a custom made sorting algorithm and support different ways to sort the data, then you just have to change the way you compare your data. This mean, in your current code, change this part
if (arr[j].time < arr[min].time) {
min = j;
}
To something more generic like
if (compare(arr[j], arr[min]) < 0) {
min = j;
}
Where you only need to change the implementation of the compare method by the one you need. Still, it will be too complex to create and maintain a method that can support different ways to compare the data. So the best option seems to be a Comparator<showInfo>, making your code look like this:
if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
min = j;
}
where the showInfoComparator holds the logic to compare the elements. Now your intSort would become into something more generic:
public static void genericSort(Comparator<showInfo> showInfoComparator) {
//your current implementation with few modifications
//...
//using the comparator to find the minimum element
if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
min = j;
}
//...
//swapping the elements directly in the array instead of swapping part of the data
if (min != i) {
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
//...
}
Now, you just have to write a set of Comparator<showInfo> implementations that supports your custom criteria. For example, here's one that compares showInfo instances using the time field:
public class ShowInfoTimeComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
}
}
Another comparator that uses the name field:
public class ShowInfoNameComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
return showInfo1.getName().compareTo(showInfo2.getName());
}
}
Now in your code you can call it like this1:
if (*compare by time*) {
genericSort(showInfoArray, new ShowInfoTimeComparator());
}
if (*compare by name*) {
genericSort(showInfoArray, new ShowInfoNameComparator());
}
if (*another custom rule*) {
genericSort(showInfoArray, new ShowInfoAnotherCustomRuleComparator());
}
where now you can implement a custom rule like compare showInfo objects using two or more fields. Taking as example your name and day fields (as stated in the question):
public class ShowInfoNameAndDayComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
int nameComparisonResult = showInfo1.getName().compareTo(showInfo2.getName());
if (nameComparisonResult == 0) {
return showInfo1.getDay().compareTo(showInfo2.getDay());
}
return nameComparisonResult;
}
}
1: There are other ways to solve this instead using lot of if statements, but looks like that's outside the question scope. If not, edit the question and add it to show another ways to solve this.
Other tips for your current code:
Declare the names of the classes using CamelCase, where the first letter of the class name is Upper Case, so your showInfo class must be renamed to ShowInfo.
To access to the fields of a class, use proper getters and setters instead of marking the fields as public or leaving the with default scope. This mean, your ShowInfo class should become into:
public class ShowInfo {
private String name;
private String day;
private int time;
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
//similar for other fields in the class
}
Use selection sort algorithm which is easy to implement,
for (int i = 0; i < arr.length; i++)
{
for (int j = i + 1; j < arr.length; j++)
{
if (arr[i].time > arr[j].time) // Here ur code that which should be compare
{
ShowInfo temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
no need to check min element. go through this wiki http://en.wikipedia.org/wiki/Selection_sort
Why not you use a Collection for this sort of a thingy to work. Moreover, in your added example, you are simply changing one attribute of a given object, while sorting, though you not changing the position of the object as a whole, inside the given list.
Create a List which will contain the references of all the Shows, now compare each attribute of one Show with another, in the List. Once the algorithm feels like, that swapping needs to be done, simply pick the reference from the List, save it in a temp variable, replace it with a new reference at this location, and set duplicate to the one stored in the temp variable. You are done, List is sorted :-)
Here is one small example for the same, for help :
import java.io.*;
import java.util.*;
public class Sorter {
private BufferedReader input;
private List<ShowInfo> showList;
public Sorter() {
showList = new ArrayList<ShowInfo>();
input = new BufferedReader(
new InputStreamReader((System.in)));
}
private void createList() throws IOException {
for (int i = 0; i < 5; i++) {
System.out.format("Enter Show Name :");
String name = input.readLine();
System.out.format("Enter Time of the Show : ");
int time = Integer.parseInt(input.readLine());
ShowInfo show = new ShowInfo(name, time);
showList.add(show);
}
}
private void performTask() {
try {
createList();
} catch (Exception e) {
e.printStackTrace();
}
sortByTime(showList);
}
private void sortByTime(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
if (showList.get(j).getTime() <
showList.get(min).getTime()) {
min = j;
}
}
if (min != i) {
ShowInfo temp = showList.get(i);
showList.set(i, showList.get(min));
showList.set(min, temp);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
public static void main(String[] args) {
new Sorter().performTask();
}
}
class ShowInfo {
private String name;
int time;
public ShowInfo(String n, int t) {
name = n;
time = t;
}
public String getName() {
return name;
}
public int getTime() {
return time;
}
}
EDIT 2 :
For sorting By Name you can use this function :
private void sortByName(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
int value = (showList.get(j).getName()).compareToIgnoreCase(
showList.get(min).getName());
if (value < 0)
min = j;
}
if (min != i) {
ShowInfo temp = showList.get(i);
showList.set(i, showList.get(min));
showList.set(min, temp);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
EDIT 3 :
Added Comparable<?> Interface, to the existing class to perform sorting based on specified input. Though one can improve on the logic, by using Enumeration, though leaving it for the OP to try his/her hands on :-)
import java.io.*;
import java.util.*;
public class Sorter {
private BufferedReader input;
private List<ShowInfo> showList;
private int command;
public Sorter() {
showList = new ArrayList<ShowInfo>();
input = new BufferedReader(
new InputStreamReader((System.in)));
command = -1;
}
private void createList() throws IOException {
for (int i = 0; i < 5; i++) {
System.out.format("Enter Show Name :");
String name = input.readLine();
System.out.format("Enter Time of the Show : ");
int time = Integer.parseInt(input.readLine());
ShowInfo show = new ShowInfo(name, time);
showList.add(show);
}
}
private void performTask() {
try {
createList();
} catch (Exception e) {
e.printStackTrace();
}
System.out.format("How would you like to sort : %n");
System.out.format("Press 0 : By Name%n");
System.out.format("Press 1 : By Time%n");
try {
command = Integer.parseInt(input.readLine());
} catch (Exception e) {
e.printStackTrace();
}
sortList(showList);
}
private void sortList(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
showList.get(j).setValues(command);
int value = showList.get(j).compareTo(showList.get(min));
if (value < 0) {
min = j;
}
}
if (min != i) {
Collections.swap(showList, i, min);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
public static void main(String[] args) {
new Sorter().performTask();
}
}
class ShowInfo implements Comparable<ShowInfo> {
private String name;
private int time;
private int command;
public ShowInfo(String n, int t) {
name = n;
time = t;
}
public String getName() {
return name;
}
public int getTime() {
return time;
}
public void setValues(int cmd) {
command = cmd;
}
public int compareTo(ShowInfo show) {
int lastCmp = 1;
if (command == 0) {
lastCmp = name.compareTo(show.name);
} else if (command == 1) {
if (time < show.time) {
lastCmp = -1;
} else if (time == show.time) {
lastCmp = 0;
} else if (time > show.time) {
lastCmp = 1;
}
}
return lastCmp;
}
}