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/*
* Copyright 2016 Anton Tananaev (anton@traccar.org)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.traccar.helper;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class LocationTree {
public static class Item {
private Item left, right;
private float x, y;
private String data;
public Item(float x, float y) {
this(x, y, null);
}
public Item(float x, float y, String data) {
this.x = x;
this.y = y;
this.data = data;
}
public String getData() {
return data;
}
private float squaredDistance(Item item) {
return (x - item.x) * (x - item.x) + (y - item.y) * (y - item.y);
}
private float axisSquaredDistance(Item item, int axis) {
if (axis == 0) {
return (x - item.x) * (x - item.x);
} else {
return (y - item.y) * (y - item.y);
}
}
}
private Item root;
private ArrayList<Comparator<Item>> comparators = new ArrayList<>();
public LocationTree(List<Item> items) {
comparators.add(new Comparator<Item>() {
@Override
public int compare(Item o1, Item o2) {
return Float.compare(o1.x, o2.x);
}
});
comparators.add(new Comparator<Item>() {
@Override
public int compare(Item o1, Item o2) {
return Float.compare(o1.y, o2.y);
}
});
root = createTree(items, 0);
}
private Item createTree(List<Item> items, int depth) {
if (items.isEmpty()) {
return null;
}
Collections.sort(items, comparators.get(depth % 2));
int currentIndex = items.size() / 2;
Item median = items.get(currentIndex);
median.left = createTree(new ArrayList<>(items.subList(0, currentIndex)), depth + 1);
median.right = createTree(new ArrayList<>(items.subList(currentIndex + 1, items.size())), depth + 1);
return median;
}
public Item findNearest(Item search) {
return findNearest(root, search, 0);
}
private Item findNearest(Item current, Item search, int depth) {
int direction = comparators.get(depth % 2).compare(search, current);
Item next, other;
if (direction < 0) {
next = current.left;
other = current.right;
} else {
next = current.right;
other = current.left;
}
Item best = current;
if (next != null) {
best = findNearest(next, search, depth + 1);
}
if (current.squaredDistance(search) < best.squaredDistance(search)) {
best = current;
}
if (other != null && current.axisSquaredDistance(search, depth % 2) < best.squaredDistance(search)) {
Item possibleBest = findNearest(other, search, depth + 1);
if (possibleBest.squaredDistance(search) < best.squaredDistance(search)) {
best = possibleBest;
}
}
return best;
}
}
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