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Implement PairPriorityQueue wrapper
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package org.pgpainless.wot.dijkstra
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import java.util.PriorityQueue
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/**
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* A de-duplicating max-priority queue for key-value pairs.
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*
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* When an element is popped, the queue entry with the *largest value*
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* is popped (if there are multiple elements with the same max value,
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* one of them is returned.)
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*
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* When inserting an element, if there is already an element with the same
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* key, the element with the larger value is kept.
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*/
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internal class PairPriorityQueue<K, V : Comparable<V>>() {
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// NOTE: This implementation is not optimized for efficient inserts!
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// - Each insert() involves a linear search by key
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// - Each insert() sorts eagerly (via j.u.PriorityQueue.add())
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private val pq: PriorityQueue<Pair<K, V>> = PriorityQueue {
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// Order priority queue entries by value (max first)
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o1, o2 ->
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o2.second.compareTo(o1.second)
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}
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fun insert(key: K, value: V) {
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when (val element = pq.find { it.first == key }) {
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null -> pq.add(Pair(key, value)) // Add as a new element
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else -> {
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// If the new value is bigger: replace the element
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if (value > element.second) {
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pq.remove(element)
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pq.add(Pair(key, value))
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}
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}
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}
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}
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fun pop(): Pair<K, V>? = pq.poll()
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}
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package org.pgpainless.wot.dijkstra
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import kotlin.test.Test
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import kotlin.test.assertEquals
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// Priority queue tests.
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// Test data from `sequoia-wot:src/priority_queue.rs`.
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class PriorityQueueTest {
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@Test
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fun simple1() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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pq.insert(0, 0);
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pq.insert(1, 1);
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pq.insert(2, 2);
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pq.insert(3, 3);
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pq.insert(4, 4);
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pq.insert(5, 5);
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assertEquals(pq.pop(), Pair(5, 5));
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assertEquals(pq.pop(), Pair(4, 4));
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assertEquals(pq.pop(), Pair(3, 3));
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assertEquals(pq.pop(), Pair(2, 2));
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assertEquals(pq.pop(), Pair(1, 1));
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assertEquals(pq.pop(), Pair(0, 0));
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assertEquals(pq.pop(), null);
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assertEquals(pq.pop(), null);
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}
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@Test
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fun simple2() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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pq.insert(0, 0);
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pq.insert(1, -1);
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pq.insert(2, -2);
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pq.insert(3, -3);
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pq.insert(4, -4);
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pq.insert(5, -5);
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assertEquals(pq.pop(), Pair(0, 0));
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assertEquals(pq.pop(), Pair(1, -1));
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assertEquals(pq.pop(), Pair(2, -2));
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assertEquals(pq.pop(), Pair(3, -3));
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assertEquals(pq.pop(), Pair(4, -4));
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assertEquals(pq.pop(), Pair(5, -5));
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assertEquals(pq.pop(), null);
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assertEquals(pq.pop(), null);
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}
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@Test
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fun simple3() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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pq.insert(0, 0);
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pq.insert(1, 1);
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pq.insert(5, 5);
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pq.insert(2, 2);
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pq.insert(4, 4);
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pq.insert(3, 3);
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assertEquals(pq.pop(), Pair(5, 5));
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assertEquals(pq.pop(), Pair(4, 4));
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assertEquals(pq.pop(), Pair(3, 3));
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assertEquals(pq.pop(), Pair(2, 2));
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assertEquals(pq.pop(), Pair(1, 1));
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assertEquals(pq.pop(), Pair(0, 0));
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assertEquals(pq.pop(), null);
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assertEquals(pq.pop(), null);
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}
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@Test
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fun simple4() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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assertEquals(pq.pop(), null);
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pq.insert(0, 0);
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pq.insert(0, 0);
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assertEquals(pq.pop(), Pair(0, 0));
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assertEquals(pq.pop(), null);
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}
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@Test
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fun simple5() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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assertEquals(pq.pop(), null);
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pq.insert(0, 0);
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pq.insert(0, 0);
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assertEquals(pq.pop(), Pair(0, 0));
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pq.insert(0, 0);
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assertEquals(pq.pop(), Pair(0, 0));
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assertEquals(pq.pop(), null);
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}
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@Test
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fun duplicates() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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// Insert different keys with the same value.
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for (i in 0 until 20) {
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pq.insert(i, 0);
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}
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// Insert the same keys with their own value. This should
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// overwrite the old keys.
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for (i in 0 until 20) {
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pq.insert(i, i);
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}
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// Insert different keys with the same value.
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for (i in 0 until 20) {
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pq.insert(i, 0);
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}
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for (i in 19 downTo 0) {
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assertEquals(pq.pop(), Pair(i, i));
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}
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assertEquals(pq.pop(), null);
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assertEquals(pq.pop(), null);
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}
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@Test
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fun insert_pop() {
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val pq: PairPriorityQueue<Int, Int> = PairPriorityQueue();
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// Insert different keys with the same value.
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for (i in 0 until 10) {
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pq.insert(i, 0);
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}
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// Insert the same keys with their own value. This should
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// overwrite the old keys.
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for (i in 9 downTo 0) {
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pq.insert(i, i);
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assertEquals(pq.pop(), Pair(i, i));
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}
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assertEquals(pq.pop(), null);
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assertEquals(pq.pop(), null);
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}
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}
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