Sorted List binarySearch functions

src/main/java/org/apache/commons/collections4/ListUtils.java

@@ -24,6 +24,7 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Objects;
+import java.util.function.Function;
 
 import org.apache.commons.collections4.bag.HashBag;
 import org.apache.commons.collections4.functors.DefaultEquator;
@@ -132,6 +133,221 @@ public int size() {
         }
     }
 
+    /**
+     * Searches element in list sorted by key.  If there are multiple elements matching, it returns first occurrence.
+     * If the list is not sorted, the result is undefined.
+     *
+     * @param list
+     *      list sorted by key field
+     * @param key
+     *      key to search for
+     * @param keyExtractor
+     *      function to extract key from element
+     * @param comparator
+     *      comparator for keys
+     *
+     * @return
+     *      index of the first occurrence of search key, if it is contained in the list; otherwise,
+     *      (-first_greater - 1). The first_greater is the index of lowest greater element in the list - if all elements
+     *      are lower, the first_greater is defined as list.size().
+     *
+     * @param <T>
+     *     type of list element
+     * @param <K>
+     *     type of key
+     */
+    public static <K, T> int binarySearchFirst(
+            List<T> list,
+            K key,
+            Function<T, K> keyExtractor, Comparator<? super K> comparator
+    ) {
+        return binarySearchFirst0(list, 0, list.size(), key, keyExtractor, comparator);
+    }
+
+    /**
+     * Searches element in list sorted by key, within range fromIndex (inclusive) - toIndex (exclusive).  If there are
+     * multiple elements matching, it returns first occurrence.  If the list is not sorted, the result is undefined.
+     *
+     * @param list
+     *      list sorted by key field
+     * @param fromIndex
+     *      start index (inclusive)
+     * @param toIndex
+     *      end index (exclusive)
+     * @param key
+     *      key to search for
+     * @param keyExtractor
+     *      function to extract key from element
+     * @param comparator
+     *      comparator for keys
+     *
+     * @return
+     *      index of the first occurrence of search key, if it is contained in the list within specified range;
+     *      otherwise, (-first_greater - 1).  The first_greater is the index of lowest greater element in the list - if
+     *      all elements are lower, the first_greater is defined as toIndex.
+     *
+     * @throws ArrayIndexOutOfBoundsException
+     *      when fromIndex or toIndex is out of array range
+     * @throws IllegalArgumentException
+     *      when fromIndex is greater than toIndex
+     *
+     * @param <T>
+     *     type of list element
+     * @param <K>
+     *     type of key
+     */
+    public static <T, K> int binarySearchFirst(
+            List<T> list,
+            int fromIndex, int toIndex,
+            K key,
+            Function<T, K> keyExtractor, Comparator<? super K> comparator
+    ) {
+        checkRange(list.size(), fromIndex, toIndex);
+
+        return binarySearchFirst0(list, fromIndex, toIndex, key, keyExtractor, comparator);
+    }
+
+    // common implementation for binarySearch methods, with same semantics:
+    private static <T, K> int binarySearchFirst0(
+            List<T> list,
+            int fromIndex, int toIndex,
+            K key,
+            Function<T, K> keyExtractor, Comparator<? super K> comparator
+    ) {
+        int l = fromIndex;
+        int h = toIndex - 1;
+
+        while (l <= h) {
+            final int m = (l + h) >>> 1; // unsigned shift to avoid overflow
+            final K value = keyExtractor.apply(list.get(m));
+            final int c = comparator.compare(value, key);
+            if (c < 0) {
+                l = m + 1;
+            } else if (c > 0) {
+                h = m - 1;
+            } else if (l < h) {
+                // possibly multiple matching items remaining:
+                h = m;
+            } else {
+                // single matching item remaining:
+                return m;
+            }
+        }
+
+        // not found, the l points to the lowest higher match:
+        return -l - 1;
+    }
+
+    /**
+     * Searches element in list sorted by key.  If there are multiple elements matching, it returns last occurrence.
+     * If the list is not sorted, the result is undefined.
+     *
+     * @param list
+     *      list sorted by key field
+     * @param key
+     *      key to search for
+     * @param keyExtractor
+     *      function to extract key from element
+     * @param comparator
+     *      comparator for keys
+     *
+     * @return
+     *      index of the last occurrence of search key, if it is contained in the list; otherwise,
+     *      (-first_greater - 1). The first_greater is the index of lowest greater element in the list - if all elements
+     *      are lower, the first_greater is defined as list.size() .
+     *
+     * @param <T>
+     *     type of array element
+     * @param <K>
+     *     type of key
+     */
+    public static <K, T> int binarySearchLast(
+            List<T> list,
+            K key,
+            Function<T, K> keyExtractor, Comparator<? super K> comparator
+    ) {
+        return binarySearchLast0(list, 0, list.size(), key, keyExtractor, comparator);
+    }
+
+    /**
+     * Searches element in list sorted by key, within range fromIndex (inclusive) - toIndex (exclusive).  If there are
+     * multiple elements matching, it returns last occurrence.  If the list is not sorted, the result is undefined.
+     *
+     * @param list
+     *      list sorted by key field
+     * @param fromIndex
+     *      start index (inclusive)
+     * @param toIndex
+     *      end index (exclusive)
+     * @param key
+     *      key to search for
+     * @param keyExtractor
+     *      function to extract key from element
+     * @param comparator
+     *      comparator for keys
+     *
+     * @return
+     *      index of the last occurrence of search key, if it is contained in the list within specified range;
+     *      otherwise, (-first_greater - 1).  The first_greater is the index of lowest greater element in the list - if
+     *      all elements are lower, the first_greater is defined as toIndex.
+     *
+     * @throws ArrayIndexOutOfBoundsException
+     *      when fromIndex or toIndex is out of array range
+     * @throws IllegalArgumentException
+     *      when fromIndex is greater than toIndex
+     *
+     * @param <T>
+     *     type of array element
+     * @param <K>
+     *     type of key
+     */
+    public static <T, K> int binarySearchLast(
+            List<T> list,
+            int fromIndex, int toIndex,
+            K key,
+            Function<T, K> keyExtractor, Comparator<? super K> comparator
+    ) {
+        checkRange(list.size(), fromIndex, toIndex);
+
+        return binarySearchLast0(list, fromIndex, toIndex, key, keyExtractor, comparator);
+    }
+
+    // common implementation for binarySearch methods, with same semantics:
+    private static <T, K> int binarySearchLast0(
+            List<T> list,
+            int fromIndex, int toIndex,
+            K key,
+            Function<T, K> keyExtractor, Comparator<? super K> comparator
+    ) {
+        int l = fromIndex;
+        int h = toIndex - 1;
+
+        while (l <= h) {
+            final int m = (l + h) >>> 1; // unsigned shift to avoid overflow
+            final K value = keyExtractor.apply(list.get(m));
+            final int c = comparator.compare(value, key);
+            if (c < 0) {
+                l = m + 1;
+            } else if (c > 0) {
+                h = m - 1;
+            } else if (m + 1 < h) {
+                // matching, more than two items remaining:
+                l = m;
+            } else if (m + 1 == h) {
+                // two items remaining, next loops would result in unchanged l and h, we have to choose m or h:
+                final K valueH = keyExtractor.apply(list.get(h));
+                final int cH = comparator.compare(valueH, key);
+                return cH == 0 ? h : m;
+            } else {
+                // one item remaining, single match:
+                return m;
+            }
+        }
+
+        // not found, the l points to the lowest higher match:
+        return -l - 1;
+    }
+
     /**
      * Returns either the passed in list, or if the list is {@code null},
      * the value of {@code defaultList}.
@@ -741,6 +957,19 @@ public static <E> List<E> unmodifiableList(final List<? extends E> list) {
         return UnmodifiableList.unmodifiableList(list);
     }
 
+    static void checkRange(int length, int fromIndex, int toIndex) {
+        if (fromIndex > toIndex) {
+            throw new IllegalArgumentException(
+                    "fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")");
+        }
+        if (fromIndex < 0) {
+            throw new ArrayIndexOutOfBoundsException(fromIndex);
+        }
+        if (toIndex > length) {
+            throw new ArrayIndexOutOfBoundsException(toIndex);
+        }
+    }
+
     /**
      * Don't allow instances.
      */

src/test/java/org/apache/commons/collections4/ListUtilsBinarySearchTest.java

@@ -0,0 +1,147 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.commons.collections4;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Timeout;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrowsExactly;
+
+/**
+ * Unit tests {@link ListUtils} binarySearch functions.
+ */
+public class ListUtilsBinarySearchTest {
+
+    @Test
+    public void binarySearchFirst_whenLowHigherThanEnd_throw() {
+        final List<Data> list = createList(0, 1);
+        assertThrowsExactly(IllegalArgumentException.class, () ->
+                ListUtils.binarySearchFirst(list, 1, 0, 0, Data::getValue, Integer::compare));
+    }
+
+    @Test
+    public void binarySearchFirst_whenLowNegative_throw() {
+        final List<Data> list = createList(0, 1);
+        assertThrowsExactly(ArrayIndexOutOfBoundsException.class, () ->
+                ListUtils.binarySearchFirst(list, -1, 0, 0, Data::getValue, Integer::compare));
+    }
+
+    @Test
+    public void binarySearchFirst_whenEndBeyondLength_throw() {
+        final List<Data> list = createList(0, 1);
+        assertThrowsExactly(ArrayIndexOutOfBoundsException.class, () ->
+                ListUtils.binarySearchFirst(list, 0, 3, 0, Data::getValue, Integer::compare));
+    }
+
+    @Test
+    public void binarySearchLast_whenLowHigherThanEnd_throw() {
+        final List<Data> list = createList(0, 1);
+        assertThrowsExactly(IllegalArgumentException.class, () ->
+                ListUtils.binarySearchLast(list, 1, 0, 0, Data::getValue, Integer::compare));
+    }
+
+    @Test
+    public void binarySearchFirst_whenEmpty_returnM1() {
+        final List<Data> list = createList();
+        final int found = ListUtils.binarySearchFirst(list, 0, Data::getValue, Integer::compare);
+        assertEquals(-1, found);
+    }
+
+    @Test
+    public void binarySearchFirst_whenExists_returnIndex() {
+        final List<Data> list = createList(0, 1, 2, 4, 7, 9, 12, 15, 17, 19, 25);
+        final int found = ListUtils.binarySearchFirst(list, 9, Data::getValue, Integer::compare);
+        assertEquals(5, found);
+    }
+
+    @Test
+    @Timeout(10)
+    public void binarySearchFirst_whenMultiple_returnFirst() {
+        final List<Data> list = createList(3, 4, 6, 6, 6, 7, 7, 8, 8, 9, 9, 9);
+        for (int i = 0; i < list.size(); ++i) {
+            if (i > 0 && list.get(i).value == list.get(i - 1).value) {
+                continue;
+            }
+            final int found = ListUtils.binarySearchFirst(list, list.get(i).value, Data::getValue, Integer::compare);
+            assertEquals(i, found);
+        }
+    }
+
+    @Test
+    @Timeout(10)
+    public void binarySearchLast_whenMultiple_returnFirst() {
+        final List<Data> list = createList(3, 4, 6, 6, 6, 7, 7, 8, 8, 9, 9, 9);
+        for (int i = 0; i < list.size(); ++i) {
+            if (i < list.size() - 1 && list.get(i).value == list.get(i + 1).value) {
+                continue;
+            }
+            final int found = ListUtils.binarySearchLast(list, list.get(i).value, Data::getValue, Integer::compare);
+            assertEquals(i, found);
+        }
+    }
+
+    @Test
+    public void binarySearchFirst_whenNotExistsMiddle_returnMinusInsertion() {
+        final List<Data> list = createList(0, 1, 2, 4, 7, 9, 12, 15, 17, 19, 25);
+        final int found = ListUtils.binarySearchFirst(list, 8, Data::getValue, Integer::compare);
+        assertEquals(-6, found);
+    }
+
+    @Test
+    public void binarySearchFirst_whenNotExistsBeginning_returnMinus1() {
+        final List<Data> list = createList(0, 1, 2, 4, 7, 9, 12, 15, 17, 19, 25);
+        final int found = ListUtils.binarySearchFirst(list, -3, Data::getValue, Integer::compare);
+        assertEquals(-1, found);
+    }
+
+    @Test
+    public void binarySearchFirst_whenNotExistsEnd_returnMinusLength() {
+        final List<Data> list = createList(0, 1, 2, 4, 7, 9, 12, 15, 17, 19, 25);
+        final int found = ListUtils.binarySearchFirst(list, 29, Data::getValue, Integer::compare);
+        assertEquals(-(list.size() + 1), found);
+    }
+
+    @Test
+    @Timeout(10)
+    public void binarySearchFirst_whenUnsorted_dontInfiniteLoop() {
+        final List<Data> list = createList(7, 1, 4, 9, 11, 8);
+        final int found = ListUtils.binarySearchFirst(list, 10, Data::getValue, Integer::compare);
+    }
+
+    private List<Data> createList(int... values) {
+        return IntStream.of(values).mapToObj(Data::new)
+                .collect(Collectors.toList());
+    }
+
+    static class Data {
+
+        private final int value;
+
+        Data(int value) {
+            this.value = value;
+        }
+
+        public int getValue() {
+            return value;
+        }
+    }
+}