We have an NxM grid, grid have one element named Bob. Bob can travel diagonally blocks only. The grid has some blocked blocks on which Bob can not travel. Write a function that returns on how many possible positions Bob can move. Solve this problem using BFS and submit the executable code in any programming language. In the following image example, Bob's positioning is at 9,3, and it can visit the places where Y is marked; hence your method should return 30.
Anybody any pseudocode or approach on how to solve this using BFS
Following solution is modified version of solution given by ( https://stackoverflow.com/users/10987431/dominicm00 ) on problem ( Using BFS to find number of possible paths for an object on a grid )
Map.java:
import java.awt.*;
public class Map {
public final int width;
public final int height;
private final Cell[][] cells;
private final Move[] moves;
private Point startPoint;
public Map(int[][] mapData) {
this.width = mapData[0].length;
this.height = mapData.length;
cells = new Cell[height][width];
// define valid movements
moves = new Move[]{
new Move(1, 1),
new Move(-1, 1),
new Move(1, -1),
new Move(-1, -1)
};
generateCells(mapData);
}
public Point getStartPoint() {
return startPoint;
}
public void setStartPoint(Point p) {
if (!isValidLocation(p)) throw new IllegalArgumentException("Invalid point");
startPoint.setLocation(p);
}
public Cell getStartCell() {
return getCellAtPoint(getStartPoint());
}
public Cell getCellAtPoint(Point p) {
if (!isValidLocation(p)) throw new IllegalArgumentException("Invalid point");
return cells[p.y][p.x];
}
private void generateCells(int[][] mapData) {
boolean foundStart = false;
for (int i = 0; i < mapData.length; i++) {
for (int j = 0; j < mapData[i].length; j++) {
/*
0 = empty space
1 = wall
2 = starting point
*/
if (mapData[i][j] == 2) {
if (foundStart) throw new IllegalArgumentException("Cannot have more than one start position");
foundStart = true;
startPoint = new Point(j, i);
} else if (mapData[i][j] != 0 && mapData[i][j] != 1) {
throw new IllegalArgumentException("Map input data must contain only 0, 1, 2");
}
cells[i][j] = new Cell(j, i, mapData[i][j] == 1);
}
}
if (!foundStart) throw new IllegalArgumentException("No start point in map data");
// Add all cells adjacencies based on up, down, left, right movement
generateAdj();
}
private void generateAdj() {
for (int i = 0; i < cells.length; i++) {
for (int j = 0; j < cells[i].length; j++) {
for (Move move : moves) {
Point p2 = new Point(j + move.getX(), i + move.getY());
if (isValidLocation(p2)) {
cells[i][j].addAdjCell(cells[p2.y][p2.x]);
}
}
}
}
}
private boolean isValidLocation(Point p) {
if (p == null) throw new IllegalArgumentException("Point cannot be null");
return (p.x >= 0 && p.y >= 0) && (p.y < cells.length && p.x < cells[p.y].length);
}
private class Move {
private int x;
private int y;
public Move(int x, int y) {
this.x = x;
this.y = y;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
}}
Cell.java:
import java.util.LinkedList;
public class Cell {
public final int x;
public final int y;
public final boolean isWall;
private final LinkedList<Cell> adjCells;
public Cell(int x, int y, boolean isWall) {
if (x < 0 || y < 0) throw new IllegalArgumentException("x, y must be greater than 0");
this.x = x;
this.y = y;
this.isWall = isWall;
adjCells = new LinkedList<>();
}
public void addAdjCell(Cell c) {
if (c == null) throw new IllegalArgumentException("Cell cannot be null");
adjCells.add(c);
}
public LinkedList<Cell> getAdjCells() {
return adjCells;
}}
MapHelper.java:
class MapHelper {
public static int countReachableCells(Map map) {
if (map == null) throw new IllegalArgumentException("Arguments cannot be null");
boolean[][] visited = new boolean[map.height][map.width];
// subtract one to exclude starting point
return dfs(map.getStartCell(), visited) - 1;
}
private static int dfs(Cell currentCell, boolean[][] visited) {
visited[currentCell.y][currentCell.x] = true;
int touchedCells = 0;
for (Cell adjCell : currentCell.getAdjCells()) {
if (!adjCell.isWall && !visited[adjCell.y][adjCell.x]) {
touchedCells += dfs(adjCell, visited);
}
}
return ++touchedCells;
}}
Grid.java:
public class Grid{
public static void main(String args[]){
int[][] gridData = {
{0,0,0,0,0,0,0,0},
{0,1,0,0,0,1,0,0},
{0,0,0,0,1,0,0,0},
{0,0,0,0,0,0,0,0},
{0,0,0,1,0,0,1,0},
{0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,1,0},
{0,0,1,0,0,1,0,0},
{0,0,0,0,0,0,0,0},
{0,0,0,2,1,0,0,0}}; //2 is bobs position, 1 is blocked, 0 can be visited
Map grid = new Map(gridData);
MapHelper solution = new MapHelper();
System.out.println(solution.countReachableCells(grid));
}}
For original answer of similar problem visit (Using BFS to find number of possible paths for an object on a grid) for original answer.
The following code illustrates a logic I need in a Spring Reactive project:
Inputs:
var period = 3;
int [] inArr = {2, 4, 6, 7, 9, 11, 13, 16, 17, 18, 20, 22 };
Calculation:
var upbond = inArr[0] + period;
var count =0;
List<Integer> result = new ArrayList();
for(int a: inArr){
if(a <= upbond){
count++;
}else{
result.add(count);
count = 1;
upbond += period;
}
}
result.add(count);
System.out.println(Arrays.toString(result.toArray()));
The data source of the sorted integers is the Flux from DB where it shall continually fetch data once a new suitable data is written into the DB. And the result shall be a stream that is sending out to another node through RSocket (by the request-stream communication mode).
After some online searching on Reactor, including some tutorials, I still can't figure out how to write the logic in the Flux fashion. The difficulty I have is that those calculations on data defined outside of the loop.
How shall I approach it in the Reactor?
The scan() variant that lets you use a separately typed accumulator is your friend here.
I'd approach this with a separate State class:
public class State {
private int count;
private Optional<Integer> upbond;
private Optional<Integer> result;
public State() {
this.count = 0;
this.upbond = Optional.empty();
this.result = Optional.empty();
}
public State(int count, int upbond) {
this.count = count;
this.upbond = Optional.of(upbond);
this.result = Optional.empty();
}
public State(int count, int upbond, int result) {
this.count = count;
this.upbond = Optional.of(upbond);
this.result = Optional.of(result);
}
public int getCount() {
return count;
}
public Optional<Integer> getUpbond() {
return upbond;
}
public Optional<Integer> getResult() {
return result;
}
}
...and then use scan() to build up the state element by element:
sourceFlux
.concatWithValues(0)
.scan(new State(), (state, a) ->
a <= state.getUpbond().orElse(a + period) ?
new State(state.getCount() + 1, state.getUpbond().orElse(a + period)) :
new State(1, state.getUpbond().orElse(a + period) + period, state.getCount())
)
.windowUntil(s -> s.getResult().isPresent())
.flatMap(f -> f.reduce((s1, s2) -> s1.getResult().isPresent()?s1:s2).map(s -> s.getResult().orElse(s.getCount() - 1)))
Aside: The concatWithValues() / windowUntil() / flatMap() bits are there to handle the last element - there's probably a cleaner way of achieving that, if I think of it I'll edit the answer.
I think scan is definitely the right tool here, combined with a stateful class, although my approach would be slightly different than Michaels.
Accumulator:
class UpbondAccumulator{
final Integer period;
Integer upbond;
Integer count;
Boolean first;
Queue<Integer> results;
UpbondAccumulator(Integer period){
this.period = period;
this.count = 0;
this.upbond = 0;
this.results = new ConcurrentLinkedQueue<>();
this.first = true;
}
//Logic is inside accumulator, since accumulator is the only the only thing
//that needs it. Allows reuse of accumulator w/o code repetition
public UpbondAccumulator process(Integer in){
//If impossible value
//Add current count to queue and return
//You will have to determine what is impossible
//Since we concat this value on the end of flux
//It will signify the end of processing
//And emit the last count
if(in<0){
results.add(count);
return this;
}
//If first value
//Do stuff outside loop
if(this.first) {
upbond = in + period;
first=false;
}
//Same as your loop
if(in <= upbond)
count++;
else {
results.add(count);
count = 1;
upbond += period;
}
//Return accumulator
//This could be put elsewhere since it isn't
//Immediately obvious that `process` should return
//the object but is simpler for example
return this;
}
public Mono<Integer> getResult() {
//Return mono empty if queue is empty
//Otherwise return queued result
return Mono.justOrEmpty(results.poll());
}
}
Usage:
dbFlux
//Concat with impossible value
.concatWithValues(-1)
//Create accumulator, process value and return
.scan(new UpbondAccumulator(period), UpbondAccumulator::process)
//Get results, note if there are no results, this will be empty
//meaning it isn't passed on in chain
.flatMap(UpbondAccumulator::getResult)
Following comment from Michael here is an immutable approach
Accumulator:
public class UpbondAccumulator{
public static UpbondState process(int period,Integer in,UpbondState previous){
Integer upbond = previous.getUpbond().orElse(in + period);
int count = previous.getCount();
if(in<0) return new UpbondState(upbond, count, count);
if(in <= upbond) return new UpbondState(upbond,count + 1 , null);
return new UpbondState(upbond + period, 1, count);
}
}
State object:
public class UpbondState {
private final Integer upbond;
private final int count;
private final Integer result;
public UpbondState() {
this.count = 0;
this.upbond = null;
this.result = null;
}
public UpbondState(Integer upbond, int count,Integer result) {
this.upbond = upbond;
this.count = count;
this.result = result;
}
public int getCount() { return count; }
public Optional<Integer> getUpbond() { return Optional.ofNullable(upbond); }
public Integer getResult() { return result; }
public boolean hasResult() { return result!=null; }
}
Usage:
dbFlux
.concatWithValues(-1)
.scan(new UpbondState(),
(prev, in) -> UpbondAccumulator.process(period,in,prev))
//Could be switched for Optional, but would mean one more map
//+ I personally think makes logic less clear in this scenario
.filter(UpbondState::hasResult)
.map(UpbondState::getResult)
I tried to use reverseBystack, reverseBylink and remove.. but I don't know why when i use these functions, it has error like this.
Exception in thread "main" java.lang.NullPointerException
at LinkedQueue$Node.access$200(LinkedQueue.java:44)
at LinkedQueue.reverseBylink(LinkedQueue.java:185)
at LinkedQueue.main(LinkedQueue.java:238)
void reverseByStack() - This method reverses the order of the items in the linked list (first
becomes last and last becomes first) using a stack data strucenter code hereture`
• void reverseByLinks() - This method also reverses the order of the items in the linked list.
It should not create a new list or use a stack. It should only reverse the order of the nodes by
modifying the next values for each node in the list.
• int remove(Item item) - This method scans the queue for occurrences of item and removes
them from the queue. It returns the number of items deleted from the queue.
these are what i want to make.
enter code here public class LinkedQueue<Item> implements Iterable<Item> {
private int N; // number of elements on queue
private Node first; // beginning of queue
private Node last; // end of queue
// helper linked list class
private class Node {
private Item item;
private Node next;
}
public LinkedQueue() {
first = null;
last = null;
N = 0;
assert check();
}
public boolean isEmpty() {
return first == null;
}
public int size() {
return N;
}
public Item peek() {
if (isEmpty()) throw new NoSuchElementException("Queue
underflow");
return first.item;
}
public void enqueue(Item item) {
Node oldlast = last;
last = new Node();
last.item = item;
last.next = null;
if (isEmpty()) first = last;
else oldlast.next = last;
N++;
assert check();
}
public Item dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue
underflow");
Item item = first.item;
first = first.next;
N--;
if (isEmpty()) last = null; // to avoid loitering
assert check();
return item;
}
public String toString() {
StringBuilder s = new StringBuilder();
for (Item item : this)
s.append(item + " ");
return s.toString();
}
private boolean check() {
if (N == 0) {
if (first != null) return false;
if (last != null) return false;
}
else if (N == 1) {
if (first == null || last == null) return false;
if (first != last) return false;
if (first.next != null) return false;
}
else {
if (first == last) return false;
if (first.next == null) return false;
if (last.next != null) return false;
// check internal consistency of instance variable N
int numberOfNodes = 0;
for (Node x = first; x != null; x = x.next) {
numberOfNodes++;
}
if (numberOfNodes != N) return false;
// check internal consistency of instance variable last
Node lastNode = first;
while (lastNode.next != null) {
lastNode = lastNode.next;
}
if (last != lastNode) return false;
}
return true;
}
void reverseBystack(){
Stack<Item> s = new Stack<>();
Item item;
while (s.isEmpty() != true){
item = dequeue();
s.push(item);
}
while(s.isEmpty() != true){
item = s.pop();
enqueue(item);
}
}
void reverseBylink() {
Node prev = null;
Node current = this.first;
Node next = null;
while (current != null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
prev.next = current.next;
}
int remove(Item item){
Node cur = first;
Node prev = last;
while(cur != null) {
if(cur.item.equals(item))
System.out.println(cur.item);
}
cur = cur.next;
prev = cur.next;
return 0;
}
public Iterator<Item> iterator() {
return new ListIterator();
}
private class ListIterator implements Iterator<Item> {
private Node current = first;
public boolean hasNext() { return current != null;
}
public void remove() { throw new
UnsupportedOperationException(); }
public Item next() {
if (!hasNext()) throw new NoSuchElementException();
Item item = current.item;
current = current.next;
return item;
}
}
/**
* Unit tests the <tt>LinkedQueue</tt> data type.
*/
public static void main(String[] args) {
LinkedQueue<String> q = new LinkedQueue<String>();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) q.reverseBylink();
else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
}
StdOut.println("(" + q.size() + " left on queue)");
}
}
This is the code I'm trying to use, which seems logical. But doesn't seem to be working.
MyAsFileName.prototype.getTotalScore = function() {
var totalScore = 0;
for (var i = 0; i < allQuestions.length; i++) {
totalScore += allQuestions[i].getCalculatedScore();
if (currentModule.allQuestions[i].parent.questionCorrect == true) {
knowledgePoints++;
} else {
knowledgePoints--;
}
}
debugLog("Total score: " + totalScore);
debugLog(knowledgePoints);
return totalScore;
}
I have allQuestions defined as below:
var allQuestions = Array();
I have knowledgePoints defined as:
this.knowledgePoints = 10;
I have questionCorrect defined as:
this.questionCorrect = false;
Second fresh attempt made with new class as answer below suggested (commented out for now until I figure out how to get working):
// package
// {
/*public class Quiz {
//public
var knowledgePoints: int = 10;
//public
var allQuestions: Array = new Array;
//public
var questionCorrect: Boolean = false;
//public
function getTotalScore(): int {
var totalScore: int = 0;
for (var i = 0; i < allQuestions.length; i++) {
totalScore += allQuestions[i].getCalculatedScore();
if (currentModule.allQuestions[i].parent.questionCorrect) {
knowledgePoints++;
} else {
knowledgePoints--;
}
}
debugLog("Total score: " + totalScore);
debugLog(knowledgePoints);
return totalScore;
}
}*/
//}
This code above outputs two errors in flash console:
Error 1. Attribute used outside of class.
Error 2. 'Int' could not be loaded.
It's a weird (and actually non-AS3 way) way to do this. Instead of creating a unnamed closure which refers weird variables from who-knows where, you should make it a normal AS3 class, something like that (in a file named Quiz.as):
package
{
public class Quiz
{
public var knowledgePoints:int = 10;
public var allQuestions:Array = new Array;
public var questionCorrect:Boolean = false;
public function getTotalScore():int
{
var totalScore:int = 0;
// Your code does not explain how you will that Array.
// It is initially an empty Array of length 0.
for (var i = 0; i < allQuestions.length; i++)
{
totalScore += allQuestions[i].getCalculatedScore();
if (currentModule.allQuestions[i].parent.questionCorrect)
{
knowledgePoints++;
}
else
{
knowledgePoints--;
}
}
// Not sure what it is.
debugLog("Total score: " + totalScore);
debugLog(knowledgePoints);
return totalScore;
}
}
}
I just started to learning from this tutorial:
https://github.com/angular/angular.dart.tutorial/wiki/Creating-a-Custom-Component
I'm just stucked with a problem, and looking for some help. The rating component does not show for me, none of the methods called (at least not at any breakpoint). Here you can see the code:
https://www.dropbox.com/s/oizzl9k6nclgoqd/SecondAngularDart.zip
Please help me with some guidence, how can I debug a situation like this? Or what the problem is?
#NgComponent(
selector:'rating',
templateUrl:'rating_component.html',
cssUrl:'rating_component.css',
publishAs:'cmp'
)
class RatingComponent {
static const String _starOnChar = "\u2605";
static const String _starOffChar = "\u2606";
static const String _starOnClass = "star-on";
static const String _starOffClass = "star-off";
List<int> stars = [];
#NgTwoWay('rating')
int rating;
#NgAttr('max-rating')
int maxRating(String max) {
stars = [];
var count = max == null ? 5 : int.parse(max);
for(var i=1; i <= count; i++) {
stars.add(i);
}
}
String starClass(int star) {
return star > rating ? _starOffClass : _starOnClass;
}
String starChar(int star) {
return star > rating ? _starOffChar : _starOnChar;
}
void handleClick(int star) {
if (star == 1 && rating == 1) {
rating = 0;
} else {
rating = star;
}
}
}
You have annotated a function with #NgAttr('max-rating'). Those data-binding annotations only work with fields or setters:
#NgAttr('max-rating')
set maxRating(String max) {
stars = [];
var count = max == null ? 5 : int.parse(max);
for(var i=1; i <= count; i++) {
stars.add(i);
}
}
Also, in starClass and starChar you access rating, which could be null:
String starClass(int star) {
if (rating != null) {
return star > rating ? _starOffClass : _starOnClass;
}
}
Okay, it was a beginner mistake, but I used the component this way:
<rating max-rating="5" rating="{{ctrl.selectedRecipe.ratings}}"></rating>
But should be used this way:
<rating max-rating="5" rating="ctrl.selectedRecipe.ratings"></rating>