1 files changed, 62 insertions, 0 deletions
diff --git a/android/guava/src/com/google/common/collect/Comparators.java b/android/guava/src/com/google/common/collect/Comparators.java
index 0c79a8c29..7ada5e538 100644
--- a/android/guava/src/com/google/common/collect/Comparators.java
+++ b/android/guava/src/com/google/common/collect/Comparators.java
@@ -17,10 +17,13 @@
 package com.google.common.collect;
 
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.collect.CollectPreconditions.checkNonnegative;
 
 import com.google.common.annotations.GwtCompatible;
 import java.util.Comparator;
 import java.util.Iterator;
+import java.util.List;
+import java.util.stream.Collector;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
@@ -107,6 +110,65 @@ public final class Comparators {
   }
 
   /**
+   * Returns a {@code Collector} that returns the {@code k} smallest (relative to the specified
+   * {@code Comparator}) input elements, in ascending order, as an unmodifiable {@code List}. Ties
+   * are broken arbitrarily.
+   *
+   * <p>For example:
+   *
+   * <pre>{@code
+   * Stream.of("foo", "quux", "banana", "elephant")
+   *     .collect(least(2, comparingInt(String::length)))
+   * // returns {"foo", "quux"}
+   * }</pre>
+   *
+   * <p>This {@code Collector} uses O(k) memory and takes expected time O(n) (worst-case O(n log
+   * k)), as opposed to e.g. {@code Stream.sorted(comparator).limit(k)}, which currently takes O(n
+   * log n) time and O(n) space.
+   *
+   * @throws IllegalArgumentException if {@code k < 0}
+   */
+  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})
+  @IgnoreJRERequirement // Users will use this only if they're already using streams.
+  static <T extends @Nullable Object> Collector<T, ?, List<T>> least(
+      int k, Comparator<? super T> comparator) {
+    checkNonnegative(k, "k");
+    checkNotNull(comparator);
+    return Collector.of(
+        () -> TopKSelector.<T>least(k, comparator),
+        TopKSelector::offer,
+        TopKSelector::combine,
+        TopKSelector::topK,
+        Collector.Characteristics.UNORDERED);
+  }
+
+  /**
+   * Returns a {@code Collector} that returns the {@code k} greatest (relative to the specified
+   * {@code Comparator}) input elements, in descending order, as an unmodifiable {@code List}. Ties
+   * are broken arbitrarily.
+   *
+   * <p>For example:
+   *
+   * <pre>{@code
+   * Stream.of("foo", "quux", "banana", "elephant")
+   *     .collect(greatest(2, comparingInt(String::length)))
+   * // returns {"elephant", "banana"}
+   * }</pre>
+   *
+   * <p>This {@code Collector} uses O(k) memory and takes expected time O(n) (worst-case O(n log
+   * k)), as opposed to e.g. {@code Stream.sorted(comparator.reversed()).limit(k)}, which currently
+   * takes O(n log n) time and O(n) space.
+   *
+   * @throws IllegalArgumentException if {@code k < 0}
+   */
+  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})
+  @IgnoreJRERequirement // Users will use this only if they're already using streams.
+  static <T extends @Nullable Object> Collector<T, ?, List<T>> greatest(
+      int k, Comparator<? super T> comparator) {
+    return least(k, comparator.reversed());
+  }
+
+  /**
    * Returns the minimum of the two values. If the values compare as 0, the first is returned.
    *
    * <p>The recommended solution for finding the {@code minimum} of some values depends on the type