From 02380503fec27e396fc97ab4c2faa6a327c7ae27 Mon Sep 17 00:00:00 2001
From: Kilian Schuettler <kilian.schuettler@knecon.com>
Date: Fri, 8 Mar 2024 09:49:13 +0100
Subject: [PATCH] RED-7141: replaced arrayList with array access

---
 .../service/NearestNeighbourService.java      | 86 ++++++++++++++-----
 1 file changed, 65 insertions(+), 21 deletions(-)

diff --git a/layoutparser-service/layoutparser-service-processor/src/main/java/com/knecon/fforesight/service/layoutparser/processor/services/docstrum/service/NearestNeighbourService.java b/layoutparser-service/layoutparser-service-processor/src/main/java/com/knecon/fforesight/service/layoutparser/processor/services/docstrum/service/NearestNeighbourService.java
index 4a8338e..78c6fb7 100644
--- a/layoutparser-service/layoutparser-service-processor/src/main/java/com/knecon/fforesight/service/layoutparser/processor/services/docstrum/service/NearestNeighbourService.java
+++ b/layoutparser-service/layoutparser-service-processor/src/main/java/com/knecon/fforesight/service/layoutparser/processor/services/docstrum/service/NearestNeighbourService.java
@@ -14,6 +14,8 @@ public class NearestNeighbourService {
 
     private static final int NUMBER_OF_NEIGHBOURS = 8;
     private static final double STEP = 16.0;
+    private int neighborInsertionIndex;
+    private int neighborCount;
 
 
     public void findNearestNeighbors(List<Character> characters) {
@@ -31,8 +33,9 @@ public class NearestNeighbourService {
 
         for (int i = 0; i < characters.size(); i++) {
 
-            List<Neighbor> candidates = new ArrayList<>();
-
+            Neighbor[] candidates = new Neighbor[maxNeighborCount + 1];
+            neighborInsertionIndex = 0;
+            neighborCount = 0;
             int start = i;
             int end = i + 1;
 
@@ -45,42 +48,83 @@ public class NearestNeighbourService {
 
                 while (start > 0 && characters.get(i).getX() - characters.get(start - 1).getX() < searchDistance) {
                     start--;
-                    candidates.add(new Neighbor(characters.get(start), characters.get(i)));
-                    clearMostDistant(candidates, maxNeighborCount);
+                    candidates[neighborInsertionIndex] = new Neighbor(characters.get(start), characters.get(i));
+                    neighborCount++;
+                    if (neighborCount > maxNeighborCount) {
+                        neighborInsertionIndex = clearMostDistant(candidates);
+                        neighborCount--;
+                    } else {
+                        neighborInsertionIndex++;
+                    }
                     newCandidatesFound = true;
                 }
 
                 while (end < characters.size() && characters.get(end).getX() - characters.get(i).getX() < searchDistance) {
-                    candidates.add(new Neighbor(characters.get(end), characters.get(i)));
-                    clearMostDistant(candidates, maxNeighborCount);
+                    candidates[neighborInsertionIndex] = new Neighbor(characters.get(end), characters.get(i));
+                    neighborCount++;
+                    if (neighborCount > maxNeighborCount) {
+                        neighborInsertionIndex = clearMostDistant(candidates);
+                        neighborCount--;
+                    } else {
+                        neighborInsertionIndex++;
+                    }
                     end++;
                     newCandidatesFound = true;
                 }
 
-                if (newCandidatesFound && candidates.size() >= maxNeighborCount) {
-                    distance = candidates.stream().mapToDouble(Neighbor::getDistance).max().orElse(Double.POSITIVE_INFINITY);
+                if (newCandidatesFound && neighborCount >= maxNeighborCount) {
+                    distance = maxDistance(candidates);
                 }
             }
-            clearMostDistant(candidates, maxNeighborCount);
-            characters.get(i).setNeighbors(new ArrayList<>(candidates));
+            if (neighborCount < maxNeighborCount) {
+                clearMostDistant(candidates);
+                neighborCount--;
+            }
+
+            List<Neighbor> candidatesList = new ArrayList<>(maxNeighborCount);
+            for (Neighbor candidate : candidates) {
+                if (candidate != null) {
+                    candidatesList.add(candidate);
+                }
+            }
+            candidatesList.sort(Comparator.comparingDouble(Neighbor::getDistance));
+            assert candidatesList.size() == maxNeighborCount;
+            characters.get(i).setNeighbors(candidatesList);
         }
     }
 
 
-    private void clearMostDistant(List<Neighbor> candidates, int maxNeighborCount) {
+    private double maxDistance(Neighbor[] candidates) {
 
-        if (candidates.size() > maxNeighborCount) {
-            double maxDistance = 0;
-            int maxIndex = 0;
-            for (int i = 0; i < candidates.size(); i++) {
-                Neighbor candidate = candidates.get(i);
-                if (candidate.getDistance() > maxDistance) {
-                    maxDistance = candidate.getDistance();
-                    maxIndex = i;
-                }
+        double maxDistance = 0;
+        for (Neighbor candidate : candidates) {
+            if (candidate == null) {
+                continue;
+            }
+            if (candidate.getDistance() > maxDistance) {
+                maxDistance = candidate.getDistance();
             }
-            candidates.remove(maxIndex);
         }
+        return maxDistance;
+    }
+
+
+    private int clearMostDistant(Neighbor[] candidates) {
+
+        double maxDistance = 0;
+        int maxIndex = 0;
+        for (int i = 0; i < candidates.length; i++) {
+            Neighbor candidate = candidates[i];
+            if (candidate == null) {
+                continue;
+            }
+            if (candidate.getDistance() > maxDistance) {
+                maxDistance = candidate.getDistance();
+                maxIndex = i;
+            }
+        }
+        candidates[maxIndex] = null;
+        return maxIndex;
     }
 
 }