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POfind nearest neighbor in recursive dfs fashion
 

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    <p>I am trying to find the nearest neighbor in recursive depth-first-fashion. There are many elements involve prior to getting to this point, to keep it simple I have only included the section that I am currently having trouble. </p> <p>My idea is to find nearest neighbor to a given point based on some threshold distance, I decided to separate the process int to two methods. One to really find if the nearest neighbor exists and other method to just call that function over and over recursively.</p> <p>I have ArrayList with double values that I treat as points... if return 0.0, means I did't find the nearest neighbor (Wondering if I really use Object, might do it once I cleanup the logic).</p> <pre><code>/** * Find the nearest neighbor based on the distance threshold. * TODO: * @param currentPoint current point in the memory. * @param threshold dynamic distance threshold. * @return return the neighbor. */ private double nearestNeighbor(double currentPoint) { HashMap&lt;Double, Double&gt; unsorted = new HashMap&lt;Double, Double&gt;(); TreeMap&lt;Double, Double&gt; sorted = null; double foundNeighbor = 0.0; for (int i = 0; i &lt; bigCluster.length; i++) { if (bigCluster[i] != 0.0 &amp;&amp; bigCluster[i] != currentPoint) { double shortestDistance = Math.abs(currentPoint - bigCluster[i]); if (shortestDistance &lt;= this.getDistanceThreshold()) unsorted.put(shortestDistance, bigCluster[i]); } } if (!unsorted.isEmpty()) { sorted = new TreeMap&lt;Double, Double&gt;(unsorted); this.setDistanceThreshold(avgDistanceInCluster()); foundNeighbor = sorted.firstEntry().getValue(); return foundNeighbor; } else { return 0.0; } } </code></pre> <p>And here is my method, that I planned on calling the above in a recursive dfs fashion. </p> <pre><code>/** * Method will check if a point belongs to a cluster based on the dynamic * threshold. */ public void isBelongToCluster(double point) { for (int i = 0; i &lt; tempList.size(); i++) { double aPointInCluster = point; cluster.add(aPointInCluster); isVisited[i].visited = true; double newNeighbor = nearestNeighbor(aPointInCluster); if (newNeighbor != 0.0) { cluster.add(newNeighbor); if (i + 1 != tempList.size() &amp;&amp; (isVisited[i].visited != true)) { isBelongToCluster(newNeighbor); } } } for (int i = 0; i &lt; cluster.size(); i++) { if (cluster.get(i) != 0.0) System.out.println("whats in the cluster -&gt; " + cluster.get(i)); } } </code></pre> <p>What I am struggling is with the recursive depth first search. In Addition to that my visitor implementation doesn't look right. </p> <p>This is how I tried to handle the visitor</p> <pre><code>public class VisitedPoint { public double point; public boolean visited; public VisitedPoint(double pointToCheck) { point = pointToCheck; visited = false; } } </code></pre> <p>then I would create a VisitedPoint object, <code>private VisitedPoint[] isVisited;</code> but when I used it in my isBelongTo() method I get a null pointer exception.</p> <p>Thanks in advance for any help. </p>
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