AK: Implement minimum BinaryHeap

This enables efficient implementations of priority queues,
and will also be used in LibCompress for efficient huffman
tree generation.

3 files changed, 218 insertions, 0 deletions

diff --git a/AK/BinaryHeap.h b/AK/BinaryHeap.h
new file mode 100644
index 0000000000..0c8be31bd0
--- /dev/null
+++ b/AK/BinaryHeap.h
@@ -0,0 +1,128 @@
+/*
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+namespace AK {
+
+template<typename K, typename V, size_t Capacity>
+class BinaryHeap {
+public:
+    BinaryHeap() = default;
+    ~BinaryHeap() = default;
+
+    // This constructor allows for O(n) construction of the heap (instead of O(nlogn) for repeated insertions)
+    BinaryHeap(K keys[], V values[], size_t size)
+    {
+        VERIFY(size <= Capacity);
+        m_size = size;
+        __builtin_memcpy(m_keys, keys, size * sizeof(K));
+        __builtin_memcpy(m_values, values, size * sizeof(V));
+
+        for (ssize_t i = size / 2; i >= 0; i--) {
+            heapify_down(i);
+        }
+    }
+
+    [[nodiscard]] size_t size() const { return m_size; }
+    [[nodiscard]] bool is_empty() const { return m_size == 0; }
+
+    void insert(K key, V value)
+    {
+        VERIFY(m_size < Capacity);
+        auto index = m_size++;
+        m_keys[index] = key;
+        m_values[index] = value;
+        heapify_up(index);
+    }
+
+    V pop_min()
+    {
+        VERIFY(!is_empty());
+        auto index = --m_size;
+        swap(m_keys[0], m_keys[index]);
+        swap(m_values[0], m_values[index]);
+        heapify_down(0);
+        return m_values[index];
+    }
+
+    const V& peek_min() const
+    {
+        VERIFY(!is_empty());
+        return m_values[0];
+    }
+
+    const V& peek_min_key() const
+    {
+        VERIFY(!is_empty());
+        return m_keys[0];
+    }
+
+    void clear()
+    {
+        m_size = 0;
+    }
+
+private:
+    void heapify_down(size_t index)
+    {
+        while (index * 2 + 1 < m_size) {
+            auto left_child = index * 2 + 1;
+            auto right_child = index * 2 + 2;
+
+            auto min_child = left_child;
+            if (right_child < m_size && m_keys[right_child] < m_keys[min_child])
+                min_child = right_child;
+
+            if (m_keys[index] <= m_keys[min_child])
+                break;
+            swap(m_keys[index], m_keys[min_child]);
+            swap(m_values[index], m_values[min_child]);
+            index = min_child;
+        }
+    }
+
+    void heapify_up(size_t index)
+    {
+        while (index != 0) {
+            auto parent = (index - 1) / 2;
+
+            if (m_keys[index] >= m_keys[parent])
+                break;
+            swap(m_keys[index], m_keys[parent]);
+            swap(m_values[index], m_values[parent]);
+            index = parent;
+        }
+    }
+
+    K m_keys[Capacity];
+    V m_values[Capacity];
+    size_t m_size { 0 };
+};
+
+}
+
+using AK::BinaryHeap;
diff --git a/AK/Tests/CMakeLists.txt b/AK/Tests/CMakeLists.txt
index c7057d5a9d..3d5bc360a2 100644
--- a/AK/Tests/CMakeLists.txt
+++ b/AK/Tests/CMakeLists.txt
@@ -7,6 +7,7 @@ set(AK_TEST_SOURCES
     TestAtomic.cpp
     TestBadge.cpp
     TestBase64.cpp
+    TestBinaryHeap.cpp
     TestBinarySearch.cpp
     TestBitmap.cpp
     TestByteBuffer.cpp
diff --git a/AK/Tests/TestBinaryHeap.cpp b/AK/Tests/TestBinaryHeap.cpp
new file mode 100644
index 0000000000..43d542123a
--- /dev/null
+++ b/AK/Tests/TestBinaryHeap.cpp
@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/TestSuite.h>
+
+#include <AK/BinaryHeap.h>
+#include <AK/String.h>
+
+TEST_CASE(construct)
+{
+    BinaryHeap<int, int, 5> empty;
+    EXPECT(empty.is_empty());
+    EXPECT(empty.size() == 0);
+}
+
+TEST_CASE(construct_from_existing)
+{
+    int keys[] = { 3, 2, 1 };
+    char values[] = { 'c', 'b', 'a' };
+    BinaryHeap<int, char, 5> from_existing(keys, values, 3);
+    EXPECT(from_existing.size() == 3);
+    EXPECT_EQ(from_existing.pop_min(), 'a');
+    EXPECT_EQ(from_existing.pop_min(), 'b');
+    EXPECT_EQ(from_existing.pop_min(), 'c');
+}
+
+TEST_CASE(populate_int)
+{
+    BinaryHeap<int, int, 5> ints;
+    ints.insert(1, 10);
+    ints.insert(3, 20);
+    ints.insert(2, 30);
+    EXPECT_EQ(ints.size(), 3u);
+    EXPECT_EQ(ints.pop_min(), 10);
+    EXPECT_EQ(ints.size(), 2u);
+    EXPECT_EQ(ints.pop_min(), 30);
+    EXPECT_EQ(ints.size(), 1u);
+    EXPECT_EQ(ints.pop_min(), 20);
+    EXPECT_EQ(ints.size(), 0u);
+}
+
+TEST_CASE(populate_string)
+{
+    BinaryHeap<int, String, 5> strings;
+    strings.insert(1, "ABC");
+    strings.insert(2, "DEF");
+    EXPECT_EQ(strings.size(), 2u);
+    EXPECT_EQ(strings.pop_min(), "ABC");
+    EXPECT_EQ(strings.pop_min(), "DEF");
+    EXPECT(strings.is_empty());
+}
+
+TEST_CASE(large_populate_reverse)
+{
+    BinaryHeap<int, int, 1024> ints;
+    for (int i = 1023; i >= 0; i--) {
+        ints.insert(i, i);
+    }
+    EXPECT_EQ(ints.size(), 1024u);
+    for (int i = 0; i < 1024; i++) {
+        EXPECT_EQ(ints.peek_min(), i);
+        EXPECT_EQ(ints.pop_min(), i);
+    }
+}
+
+TEST_MAIN(BinaryHeap)