How to find 3 closest coordinates from a point in an array Java

Question

I have a homework assignment that and I am completely stuck (level: beginner).

I have to create a method that finds 3 closest distances from an user entry and all the points in an array - and I am stuck here.

The method is: public static int[] troisPlusProches (int x, int y, int[] coordonneesHabitations) where int x and int y are user entries, and the array int[] coordonneesHabitations is int[] coordonneesHabitations = {9, 30, 18, 8, 3, 18, 25, 36}. So the points are (9,30), (18,8), (3,18) and (25,36).

I used the formula: distance = Math.sqrt(((x1 - x2) * (x1 - x2)) + ((y1 - y2) * (y1 - y2))) to calculate the distances.

And now i have to find 3 shortest distances from an user entries and return their positions in a new array.

So if the user entries are x=10, y=15.

The shortest distance is 7.616 from a point (3, 18), the next one is 10.630 from a point (18, 8), and the third one is 15.033 from a point (9, 30). In this case the method should return an array int[] troisPlusProches = {3, 18, 18, 8, 9, 30}.

I know what I have to do, I just can't figure out how...

Here's one of the many wrong attempts:

public static int[] troisPlusProches (int x, int y, int[] (coordonneesHabitations) 
{
    int [] that = Arrays.copyOf(coordonneesHabitations, coordonneesHabitations.length);
    int table[] = new int[6];
    double distanceA = 0.0; 
    double minDistance = Float.MAX_VALUE;
    int a = 0;
    int b = 0;
    int i = 0;
    double ignore = Float.MAX_VALUE;
    double ignore2 = Float.MAX_VALUE;

    for (i = 0; i < that.length; i += 2) {
           a = that[i];
           b = that[i+1]; 
           distanceA = calculerDistance(a, b, x, y);
           if (distanceA < minDistance) { 
               minDistance = distanceA;
               table[0] = a;
               table[1] = b;
           }
       }
    ignore = minDistance;


    for (i = 0; i < that.length; i += 2) {
           a = that[i];
           b = that[i+1]; 
           distanceA = calculerDistance(a, b, x, y);
           if (distanceA == ignore) {
               continue; 
               }
           if (distanceA < minDistance) { 
               minDistance = distanceA;
               table[2] = a;
               table[3] = b;
               } 
           }
    ignore2 = minDistance;

    for (i = 0; i < that.length; i += 2) {
           a = that[i];
           b = that[i+1]; 
           distanceA = calculerDistance(a, b, x, y);
           if ((distanceA == ignore) || (distanceA == ignore2)) {
               continue; 
               }
           if (distanceA < minDistance) { 
               minDistance = distanceA;
               table[2] = a;
               table[3] = b;
               } 
           }

    return table; 
    }

Answer 1

I don't speak french so I find it hard to read your code. However, think about it like this:

Tou have a method which computes the closest point to a user entry. Now you need to create a copy of that method which allows you to compute the closest point to a user entry excluding the point you already found. That will let you find the first and second closest points. Then do the same thing to find the third point, this time by excluding the two points you already found.

You can make a copy of your existing method. It might look something like this:

public static int plusProche (int x, int y, int[] coordonneesHabitations, int ignoreIndex) {
    double distanceA = 0.0; 
    int k = x;
    int z = y;
    int a = 0;
    int b = 0;
    int [] that = Arrays.copyOf(coordonneesHabitations, coordonneesHabitations.length); 
    int taille = that.length;
    int i = 0;
    double minDistance = Float.MAX_VALUE;
    int position = 0;

       for (i = 0; i < taille; i += 2) {

           //here we add the ability to skip the passed index
           if ((i / 2) == ignoreIndex) {
               continue;
           }

           a = that[i];
           b = that[i+1]; 
           distanceA = calculerDistance(a, b, k, z);
           if (distanceA < minDistance) { 
               minDistance = distanceA;
               position = i/2;
               System.out.println(i + " " + minDistance);
           }
       }
       return position;
}

You can use the above to find the second closest point, by passing the index of the closest point as an argument. It will skip that index, therefore finding the next closest index. Do something similar to find the third closest point.

Answer 2

There's a solution that works, in case someone might need it...

public static int[] troisPlusProches (int x, int y, int[] coordonneesHabitations) 
{
    LinkedList<Integer> resultArray = new LinkedList<Integer>();
    int[] origArr = Arrays.copyOf(coordonneesHabitations, coordonneesHabitations.length);
    while (resultArray.size() < 6) {
        int positionInArray = Decharge.plusProche(x, y, origArr);
        LinkedList<Integer> newArr = new LinkedList<Integer>();
        for (int i = 0; i < origArr.length; i = i + 2) {
            if (i != positionInArray * 2) {
                newArr.add(origArr[i]);
                newArr.add(origArr[i + 1]);
            } else {
                resultArray.add(origArr[i]);
                resultArray.add(origArr[i + 1]);
            }
        }
        origArr = new int[newArr.size()];
        for (int k = 0; k < origArr.length; k++) {
            origArr[k] = newArr.get(k);
        }
    }
    int[] intResultArray = new int[resultArray.size()];
    for (int l = 0; l < intResultArray.length; l++) {
        intResultArray[l] = resultArray.get(l);
    }
    return intResultArray;