binary heap impl

Algorithms/Algorithms.Tests/BinaryHeapTests/BinaryHeapTests.cs

@@ -0,0 +1,68 @@
+using System.Collections.Generic;
+using System.Data;
+using Xunit;
+
+namespace Algorithms.Tests
+{
+    public class BinaryHeapTests
+    {
+        [Fact]
+        public void Can_not_remove_root_from_empty_heap()
+        {
+            var heap = new BinaryHeap<int>();
+            Assert.Throws<DataException>(() => heap.RemoveRoot());
+        }
+
+        [Fact]
+        public void Heap_size_should_increase_after_add()
+        {
+            var heap = new BinaryHeap<int>();
+            heap.Add(42);
+            Assert.True(heap.Size == 1);
+        }
+
+        [Fact]
+        public void Heap_size_should_decrease_after_remove()
+        {
+            var heap = new BinaryHeap<int>(new List<int>{1, 2, 3});
+            heap.RemoveRoot();
+            Assert.True(heap.Size == 2);
+        }
+
+        [Theory]
+        [InlineData(new int[] {}, 0)]
+        [InlineData(new [] {1, 2, 3}, 3)]
+        [InlineData(new [] {42}, 1)]
+        public void Heap_size_should_be_equal_to_array_length(int[] source, int expectedSize)
+        {
+            var heap = new BinaryHeap<int>(source);
+            Assert.True(heap.Size == expectedSize);
+        }
+
+        [Theory]
+        [InlineData(new [] {1}, 1)]
+        [InlineData(new [] {1, 2, 3}, 3, 2, 1)]
+        [InlineData(new [] {42, 3, 67, -10}, 67, 42)]
+        public void Root_should_always_be_max_in_MaxHeap(int[] data, params int[] expectedValues)
+        {
+            var heap = new BinaryHeap<int>(data, HeapType.MaxHeap);
+            foreach (var value in expectedValues)
+            {
+                Assert.True(heap.RemoveRoot() == value);
+            }
+        }
+
+        [Theory]
+        [InlineData(new [] {1}, 1)]
+        [InlineData(new [] {1, 2, 3}, 1, 2, 3)]
+        [InlineData(new [] {7, 1, 54, 3, -42}, -42, 1, 3, 7, 54)]
+        public void Root_should_always_be_min_in_MinHeap(int[] data, params int[] expectedValues)
+        {
+            var heap = new BinaryHeap<int>(data, HeapType.MinHeap);
+            foreach (var value in expectedValues)
+            {
+                Assert.True(heap.RemoveRoot() == value);
+            }
+        }
+    }
+}

Algorithms/Algorithms/BinaryHeap/BinaryHeap.cs

@@ -0,0 +1,114 @@
+using System;
+using System.Collections.Generic;
+using System.Data;
+using System.Linq;
+
+namespace Algorithms
+{
+    public class BinaryHeap<T> : IBinaryHeap<T>
+        where T : IComparable
+    {
+        private readonly List<T> _data;
+        private readonly HeapType _type;
+
+        public BinaryHeap(HeapType type = HeapType.MaxHeap)
+        {
+            _data = new List<T>();
+            _type = type;
+        }
+
+        public BinaryHeap(IEnumerable<T> elems, HeapType type = HeapType.MaxHeap)
+        {
+            _data = elems.ToList();
+            _type = type;
+            BuildHeap(_data);
+        }
+
+        /// <summary>
+        ///     Returns true if elements are ordered, as it's required by HeapType
+        /// </summary>
+        private Func<T, T, bool> Cmp
+        {
+            get
+            {
+                if (_type is HeapType.MaxHeap) return (a, b) => a.CompareTo(b) > 0;
+                return (a, b) => a.CompareTo(b) <= 0;
+            }
+        }
+
+        /// <summary>
+        ///     Returns size of the heap
+        /// </summary>
+        public int Size => _data.Count;
+
+        /// <summary>
+        ///     Adds element to the heap
+        /// </summary>
+        public void Add(T item)
+        {
+            _data.Add(item);
+            var current = Size - 1;
+            var parent = (current - 1) / 2;
+
+            while (current > 0 && !Cmp(_data[parent], _data[current]))
+            {
+                (_data[parent], _data[current]) = (_data[current], _data[parent]);
+                current = parent;
+                parent = (current - 1) / 2;
+            }
+        }
+
+        /// <summary>
+        ///     Removes and returns root of the heap
+        /// </summary>
+        /// <exception cref="DataException">Thrown when trying to remove from empty heap</exception>
+        public T RemoveRoot()
+        {
+            if (Size == 0) throw new DataException("Heap is empty");
+            var result = _data[0];
+            _data[0] = _data[Size - 1];
+            _data.RemoveAt(Size - 1);
+            Heapify(_data, 0);
+            return result;
+        }
+
+        /// <summary>
+        ///     Builds heap from an unordered set of data
+        /// </summary>
+        private void BuildHeap(IList<T> data)
+        {
+            for (var i = Size / 2; i >= 0; --i)
+                Heapify(data, i);
+        }
+
+        /// <summary>
+        ///     Turns unordered array into heap, with root in data[index]
+        /// </summary>
+        /// <param name="data">Array representation of heap</param>
+        /// <param name="index">Element, that is considered to be root</param>
+        private void Heapify(IList<T> data, int index)
+        {
+            while (true)
+            {
+                var l = 2 * index + 1;
+                var r = 2 * index + 2;
+                var max = index;
+                if (l < Size && !Cmp(data[max], data[l])) max = l;
+                if (r < Size && !Cmp(data[max], data[r])) max = r;
+                if (max == index) return;
+
+                (data[max], data[index]) = (data[index], data[max]);
+                index = max;
+            }
+        }
+    }
+
+    /// <summary>
+    ///     Indicates type of heap: either its root is maximum or minimum
+    /// </summary>
+    public enum HeapType
+    {
+        MaxHeap,
+        MinHeap
+    }
+}

Algorithms/Algorithms/BinaryHeap/IBinaryHeap.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace Algorithms 
+{
+    internal interface IBinaryHeap<T>
+        where T : IComparable
+    {
+        void Add(T item);
+        T RemoveRoot();
+    }
+}