diff --git a/core/src/main/java/de/danoeh/antennapod/core/util/FeedItemPermutors.java b/core/src/main/java/de/danoeh/antennapod/core/util/FeedItemPermutors.java
index 7f2742ab0..12377791e 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/util/FeedItemPermutors.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/util/FeedItemPermutors.java
@@ -8,6 +8,7 @@ import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
+import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
@@ -116,38 +117,23 @@ public class FeedItemPermutors {
* prefer a more balanced ordering that avoids having to listen to clusters of consecutive
* episodes from the same feed. This is what "Smart Shuffle" tries to accomplish.
*
- * The Smart Shuffle algorithm involves spreading episodes from each feed out over the whole
- * queue. To do this, we calculate the number of episodes in each feed, then a common multiple
- * (not the smallest); each episode is then spread out, and we sort the resulting list of
- * episodes by "spread out factor" and feed name.
+ * Assume the queue looks like this: `ABCDDEEEEEEEEEE`.
+ * This method first starts with a queue of the final size, where each slot is empty (null).
+ * It takes the podcast with most episodes (`E`) and places the episodes spread out in the queue: `EE_E_EE_E_EE_EE`.
+ * The podcast with the second-most number of episodes (`D`) is then
+ * placed spread-out in the *available* slots: `EE_EDEE_EDEE_EE`.
+ * This continues, until we end up with: `EEBEDEECEDEEAEE`.
*
- * For example, given a queue containing three episodes each from three different feeds
- * (A, B, and C), a simple pubdate sort might result in a queue that looks like the following:
- *
- * B1, B2, B3, A1, A2, C1, C2, C3, A3
- *
- * (note that feed B episodes were all published before the first feed A episode, so a simple
- * pubdate sort will often result in significant clustering of episodes from a single feed)
- *
- * Using Smart Shuffle, the resulting queue would look like the following:
- *
- * A1, B1, C1, A2, B2, C2, A3, B3, C3
- *
- * (note that episodes above aren't strictly ordered in terms of pubdate, but episodes
- * of each feed do appear in pubdate order)
+ * Note that episodes aren't strictly ordered in terms of pubdate, but episodes of each feed are.
*
* @param queue A (modifiable) list of FeedItem elements to be reordered.
* @param ascending {@code true} to use ascending pubdate in the reordering;
* {@code false} for descending.
*/
private static void smartShuffle(List queue, boolean ascending) {
-
// Divide FeedItems into lists by feed
-
Map> map = new HashMap<>();
-
- while (!queue.isEmpty()) {
- FeedItem item = queue.remove(0);
+ for (FeedItem item : queue) {
Long id = item.getFeedId();
if (!map.containsKey(id)) {
map.put(id, new ArrayList<>());
@@ -156,55 +142,43 @@ public class FeedItemPermutors {
}
// Sort each individual list by PubDate (ascending/descending)
-
Comparator itemComparator = ascending
- ? (f1, f2) -> f1.getPubDate().compareTo(f2.getPubDate())
- : (f1, f2) -> f2.getPubDate().compareTo(f1.getPubDate());
-
- // Calculate the spread
-
- long spread = 0;
+ ? (f1, f2) -> f1.getPubDate().compareTo(f2.getPubDate())
+ : (f1, f2) -> f2.getPubDate().compareTo(f1.getPubDate());
+ List> feeds = new ArrayList<>();
for (Map.Entry> mapEntry : map.entrySet()) {
- List feedItems = mapEntry.getValue();
- Collections.sort(feedItems, itemComparator);
- if (spread == 0) {
- spread = feedItems.size();
- } else if (spread % feedItems.size() != 0){
- spread *= feedItems.size();
- }
+ Collections.sort(mapEntry.getValue(), itemComparator);
+ feeds.add(mapEntry.getValue());
}
- // Create a list of the individual FeedItems lists, and sort it by feed title (ascending).
- // Doing this ensures that the feed order we use is predictable/deterministic.
+ ArrayList emptySlots = new ArrayList<>();
+ for (int i = 0; i < queue.size(); i++) {
+ queue.set(i, null);
+ emptySlots.add(i);
+ }
- List> feeds = new ArrayList<>(map.values());
- Collections.sort(feeds,
- (f1, f2) -> f1.get(0).getFeed().getTitle().compareTo(f2.get(0).getFeed().getTitle()));
-
- // Spread each episode out
- Map> spreadItems = new HashMap<>();
+ // Starting with the largest feed, place items spread out through the empty slots in the queue
+ Collections.sort(feeds, (f1, f2) -> Integer.compare(f2.size(), f1.size()));
for (List feedItems : feeds) {
- long thisSpread = spread / feedItems.size();
- if (thisSpread == 0) {
- thisSpread = 1;
- }
- // Starting from 0 ensures we front-load, so the queue starts with one episode from
- // each feed in the queue
- long itemSpread = 0;
- for (FeedItem feedItem : feedItems) {
- if (!spreadItems.containsKey(itemSpread)) {
- spreadItems.put(itemSpread, new ArrayList<>());
+ double spread = (double) emptySlots.size() / (feedItems.size() + 1);
+ Iterator emptySlotIterator = emptySlots.iterator();
+ int skipped = 0;
+ int placed = 0;
+ while (emptySlotIterator.hasNext()) {
+ int nextEmptySlot = emptySlotIterator.next();
+ skipped++;
+ if (skipped >= spread * (placed + 1)) {
+ if (queue.get(nextEmptySlot) != null) {
+ throw new RuntimeException("Slot to be placed in not empty");
+ }
+ queue.set(nextEmptySlot, feedItems.get(placed));
+ emptySlotIterator.remove();
+ placed++;
+ if (placed == feedItems.size()) {
+ break;
+ }
}
- spreadItems.get(itemSpread).add(feedItem);
- itemSpread += thisSpread;
}
}
-
- // Go through the spread items and add them to the queue
- List spreads = new ArrayList<>(spreadItems.keySet());
- Collections.sort(spreads);
- for (long itemSpread : spreads) {
- queue.addAll(spreadItems.get(itemSpread));
- }
}
}