Ch 09-02 ported from Java

.gitignore

@@ -1,14 +1,19 @@
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.
 
+# OS generated files
+.DS_Store
+.DS_Store?
+
 # User-specific files
 *.suo
 *.user
 *.userosscache
 *.sln.docstates
 
-# User-specific files (MonoDevelop/Xamarin Studio)
+# User-specific files (MonoDevelop/Xamarin Studio/VS Code)
 *.userprefs
+.vscode
 
 # Build results
 [Dd]ebug/

Ch 07. Object-Oriented Design/Ch 07. Object-Oriented Design.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp1.1</TargetFramework>
+    <RootNamespace>Chapter07</RootNamespace>
+  </PropertyGroup>
+  <ItemGroup>
+    <Folder Include="Properties\" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\ctci.Contracts\ctci.Contracts.csproj" />
+    <ProjectReference Include="..\ctci.Library\ctci.Library.csproj" />
+  </ItemGroup>
+</Project>

Ch 07. Object-Oriented Design/Q7_12_Hash_Table.cs

@@ -0,0 +1,56 @@
+using System;
+using ctci.Contracts;
+
+namespace Chapter07
+{
+    public class Q7_12_Hash_Table: Question 
+    {
+        public override void Run()
+        { 
+            Dummy bob = new Dummy("Bob", 20);
+            Dummy jim = new Dummy("Jim", 25);
+            Dummy alex = new Dummy("Alex", 30);
+            Dummy tim = new Dummy("Tim", 35);
+            Dummy maxwell = new Dummy("Maxwell", 40);
+            Dummy john = new Dummy("John", 45);
+            Dummy julie = new Dummy("Julie", 50);
+            Dummy christy = new Dummy("Christy", 55);
+            Dummy tim2 = new Dummy("Tim", 100); // This should replace the first "tim"
+
+            Dummy[] dummies = { bob, jim, alex, tim, maxwell, john, julie, christy, tim2 };
+
+            /* Test: Insert Elements. */
+            Hasher<String, Dummy> hash = new Hasher<String, Dummy>(3);
+            foreach (Dummy d in dummies)
+            {
+                Console.WriteLine(hash.Put(d.Name, d));
+            }
+
+            hash.PrintTable();
+
+            /* Test: Recall */
+            foreach (Dummy d in dummies)
+            {
+                String name = d.Name;
+                Dummy dummy = hash.Get(name);
+                if (dummy == null)
+                {
+                    Console.WriteLine($"Dummy named {name}: null");
+                }
+                else
+                {
+                    Console.WriteLine($"Dummy named {name}: {dummy}");
+                }
+                Dummy d2 = hash.Remove(name);
+                if (d2 == null)
+                {
+                    Console.WriteLine($"Dummy removed named {name}: null");
+                }
+                else
+                {
+                    Console.WriteLine($"Dummy removed named {name}: {d2}");
+                }
+            }        
+        }
+    }
+}

Ch 07. Object-Oriented Design/Q7_12_Hash_Table/Dummy.cs

@@ -0,0 +1,22 @@
+
+namespace Chapter07
+{ 
+    public class Dummy
+    {
+        public string Name { get; private set; }
+        public int Age { get; private set; }
+
+        public Dummy(string n, int a)
+        {
+            Name = n;
+            Age = a;
+        }
+
+
+        public override string ToString()
+        {
+            return "(" + Name + ", " + Age + ")";
+        }
+    }
+}
+

Ch 07. Object-Oriented Design/Q7_12_Hash_Table/Hasher.cs

@@ -0,0 +1,134 @@
+using System;
+using System.Collections.Generic;
+
+namespace Chapter07
+{ 
+    public class Hasher<K, V>
+    {
+        private class LinkedListNode<K, V>
+        {
+            public LinkedListNode<K, V> Next { get; set; }
+            public LinkedListNode<K, V> Prev { get; set; }
+            public K Key { get; set; }
+            public V Value { get; set; }
+
+            public LinkedListNode(K k, V v)
+            {
+                Key = k;
+                Value = v;
+            }
+
+            public string PrintForward()
+            {
+                string data = $"({Key},{Value})";
+                if (Next != null)
+                {
+                    return data + "->" + Next.PrintForward();
+                }
+                else
+                {
+                    return data;
+                }
+            }
+        }
+
+        private List<LinkedListNode<K, V>> _arr;
+        public Hasher(int capacity)
+        {
+            /* Create list of linked lists. */
+            _arr = new List<LinkedListNode<K, V>>();
+            for (int i = 0; i < capacity; i++)
+            {
+                _arr.Add(null);
+            }
+        }
+
+        /* Insert key and value into hash table. */
+        public V Put(K key, V value)
+        {
+            LinkedListNode<K, V> node = GetNodeForKey(key);
+            if (node != null)
+            {
+                V oldValue = node.Value;
+                node.Value = value; // just update the value.
+                return oldValue;
+            }
+
+            node = new LinkedListNode<K, V>(key, value);
+            int index = GetIndexForKey(key);
+            if (_arr[index] != null)
+            {
+                node.Next = _arr[index];
+                node.Next.Prev = node;
+            }
+            _arr[index] = node;
+            return default(V);
+        }
+
+        /* Remove node for key. */
+        public V Remove(K key)
+        {
+            LinkedListNode<K, V> node = GetNodeForKey(key);
+            if (node == null)
+            {
+                return default(V);
+            }
+
+            if (node.Prev != null)
+            {
+                node.Prev.Next = node.Next;
+            }
+            else
+            {
+                /* Removing head - update. */
+                int hashKey = GetIndexForKey(key);
+                _arr[hashKey] = node.Next;
+            }
+
+            if (node.Next != null)
+            {
+                node.Next.Prev = node.Prev;
+            }
+            return node.Value;
+        }
+
+        /* Get value for key. */
+        public V Get(K key)
+        {
+            if (key == null) return default(V);
+            LinkedListNode<K, V> node = GetNodeForKey(key);
+            return node == null ? default(V) : node.Value;
+        }
+
+        /* Get linked list node associated with a given key. */
+        private LinkedListNode<K, V> GetNodeForKey(K key)
+        {
+            int index = GetIndexForKey(key);
+            LinkedListNode<K, V> current = _arr[index];
+            while (current != null)
+            {
+                if (current.Key.Equals(key))
+                {
+                    return current;
+                }
+                current = current.Next;
+            }
+            return null;
+        }
+
+        /* Really stupid function to map a key to an index. */
+        public int GetIndexForKey(K key)
+        {
+            return Math.Abs(key.GetHashCode() % _arr.Count);
+        }
+
+        public void PrintTable()
+        {
+            for (int i = 0; i < _arr.Count; i++)
+            {
+                string s = _arr[i] == null ? string.Empty : _arr[i].PrintForward();
+                Console.WriteLine($"{i}: {s}");
+            }
+        }
+    }
+}

Ch 09. System Design and Scalability/Ch 09. System Design and Scalability.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp1.1</TargetFramework>
+    <RootNamespace>Chapter09</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Folder Include="Properties\" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\ctci.Contracts\ctci.Contracts.csproj" />
+    <ProjectReference Include="..\ctci.Library\ctci.Library.csproj" />
+  </ItemGroup>
+</Project>

Ch 09. System Design and Scalability/Q9_02_Social_Network.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Linq;
+using System.Collections.Generic;
+using ctci.Contracts;
+
+namespace Chapter09
+{
+    public class Q9_02_Social_Network : Question 
+    {
+        public static void PrintPeople(LinkedList<Person> path) {
+            if (path == null) {
+                Console.WriteLine("No path");
+            } else {
+                foreach (Person p in path) {
+                    Console.WriteLine(p.Id);
+                }
+            }		
+        }
+
+        public static bool IsEqual(LinkedList<Person> path1, LinkedList<Person> path2, bool reverse) {
+            if (path1 == null || path2 == null) {
+                return path1 == null && path2 == null;
+            }
+            if (path1.Count != path2.Count) {
+                return false;
+            }
+
+            for (int i = 0; i < path1.Count; i++) {
+                int other = reverse ? path2.Count - i - 1 : i;
+                if (path1.ElementAt(i) != path2.ElementAt(other)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+        public static bool IsEquivalent(LinkedList<Person> path1, LinkedList<Person> path2) {
+            bool f1 = IsEqual(path1, path2, false);
+            bool f2 = IsEqual(path1, path2, true);
+            return f1 || f2;
+        }	
+
+        public override void Run()
+        {
+            int nPeople = 11;
+            var people = new Dictionary<int, Person>();
+            for (int i = 0; i < nPeople; i++) {
+                Person p = new Person(i);
+                people.Add(i, p);
+            }
+
+            int[][] edges = {new[]{1, 4}, new[]{1, 2}, new[]{1, 3}, new[]{3, 2}, new[]{4, 6}, new[]{3, 7}, new[]{6, 9}, new[]{9, 10}, new[]{5, 10}, new[]{2, 5}, new[]{3, 7}};
+            //int[][] edges = {new[]{1, 4}, new[]{1, 2}, new[]{4, 6}, new[]{6, 9}, new[]{9, 10}, new[]{5, 10}, new[]{2, 5}};
+            //int[][] edges = {new[]{1, 2}, new[]{1, 4}, new[]{2, 3}, new[]{3, 4}, new[]{4, 6}, new[]{5, 6}, new[]{4, 5}}; 
+            foreach (var edge in edges) {
+                Person source = people[edge[0]];
+                source.AddFriend(edge[1]);
+
+                Person destination = people[edge[1]];
+                destination.AddFriend(edge[0]);
+            }
+
+            //int j = 4;
+            //int z = 9;
+            //LinkedList<Person> path1 = QuestionA.FindPathBFS(people, j, z);
+            //LinkedList<Person> path2 = QuestionB.FindPathBiBFS(people, j, z);
+            //Console.WriteLine("Path 1");
+            //PrintPeople(path1);
+            //Console.WriteLine("Path 2");
+            //PrintPeople(path2);
+
+            for (int i = 0; i < nPeople; i++) {
+                for (int j = 0; j < nPeople; j++) {
+                    LinkedList<Person> path1 = QuestionA.FindPathBFS(people, i, j);
+                    LinkedList<Person> path2 = QuestionB.FindPathBiBFS(people, i, j);
+                    if (!IsEquivalent(path1, path2)) {
+                        Console.WriteLine($"Not equal: {i} to {j}");
+                        Console.WriteLine("Path 1");
+                        PrintPeople(path1);
+                        Console.WriteLine("Path 2");
+                        PrintPeople(path2);
+                        break;
+                    } else {
+                        Console.WriteLine($"Is equal: {i} to {j}");
+                    }
+                }
+            }
+        }
+    }
+}

Ch 09. System Design and Scalability/Q9_02_Social_Network/BFSData.cs

@@ -0,0 +1,26 @@
+using System.Collections.Generic;
+
+namespace Chapter09
+{
+    public class BFSData 
+    {
+        public Queue<PathNode> ToVisit {get; set;}
+        public Dictionary<int, PathNode> Visited {get; set;}
+
+        public BFSData(Person root) {
+            ToVisit = new Queue<PathNode>();
+            Visited = new Dictionary<int, PathNode>();
+
+            PathNode sourcePath = new PathNode(root, null);
+            ToVisit.Enqueue(sourcePath);
+            Visited.Add(root.Id, sourcePath);	
+        }
+
+        public bool IsFinished() {
+            return ToVisit.Count == 0;
+        }
+    }
+
+}
+
+