From d84f4bad8d77e19f789599617e377988c30c8a86 Mon Sep 17 00:00:00 2001
From: Abhinav Sarkar <abhinav@abhinavsarkar.net>
Date: Fri, 28 Jun 2019 10:41:30 +0530
Subject: [PATCH] Adds LRW cache

---
 .../net/abhinavsarkar/algorist/LRWCache.java  | 80 +++++++++++++++++++
 .../algorist/OpenAddressingHashTable.java     | 64 +++++++++++++--
 2 files changed, 139 insertions(+), 5 deletions(-)
 create mode 100644 src/main/java/net/abhinavsarkar/algorist/LRWCache.java

diff --git a/src/main/java/net/abhinavsarkar/algorist/LRWCache.java b/src/main/java/net/abhinavsarkar/algorist/LRWCache.java
new file mode 100644
index 0000000..918d1da
--- /dev/null
+++ b/src/main/java/net/abhinavsarkar/algorist/LRWCache.java
@@ -0,0 +1,80 @@
+package net.abhinavsarkar.algorist;
+
+import java.util.Iterator;
+import java.util.Optional;
+
+public class LRWCache<K, V> implements Iterable<K>
+{
+
+    private final int capacity;
+    private final OpenAddressingHashTable<K, V> store;
+
+    public LRWCache(int capacity) {
+        this.capacity = capacity;
+        this.store = new OpenAddressingHashTable<>(capacity+1);
+    }
+
+    public Optional<V> get(K key) {
+        return store.get(key);
+    }
+
+    public void remove(K key) {
+        store.remove(key);
+    }
+
+    public void put(K key, V val) {
+        store.put(key, val);
+        if (store.size() > capacity) {
+            store.remove(store.iterator().next().key());
+        }
+    }
+
+    public int size()
+    {
+        return store.size();
+    }
+
+    public Iterator<K> iterator()
+    {
+        return new Iterator<K>()
+        {
+            private final Iterator<OpenAddressingHashTable.Entry<K,V>> it = store.iterator();
+
+            @Override
+            public boolean hasNext()
+            {
+                return it.hasNext();
+            }
+
+            @Override
+            public K next()
+            {
+                return it.next().key();
+            }
+        };
+    }
+
+    public String toString() {
+        return store.toString();
+    }
+
+    public static void main(String[] args)
+    {
+        LRWCache<String, String> cache = new LRWCache<>(4);
+        cache.put("a", "abhinav");
+        cache.put("b", "batman");
+        cache.put("c", "carol");
+        cache.put("z", "zellman");
+        System.out.println(cache);
+
+        cache.put("w", "walker");
+        System.out.println(cache);
+
+        cache.put("c", "carly");
+        System.out.println(cache);
+
+        cache.put("x", "xander");
+        System.out.println(cache);
+    }
+
+}
diff --git a/src/main/java/net/abhinavsarkar/algorist/OpenAddressingHashTable.java b/src/main/java/net/abhinavsarkar/algorist/OpenAddressingHashTable.java
index db52a27..96e9cab 100644
--- a/src/main/java/net/abhinavsarkar/algorist/OpenAddressingHashTable.java
+++ b/src/main/java/net/abhinavsarkar/algorist/OpenAddressingHashTable.java
@@ -9,15 +9,21 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
 
     private static final Entry REMOVED = new Entry(0,0);
     private Object[] store;
-    private ProbingStrategy probingStrategy;
+    private final ProbingStrategy probingStrategy;
     private Entry<K, V> head;
     private Entry<K, V> tail;
+    private int size;
 
     public OpenAddressingHashTable(int initialCapacity, ProbingStrategy probingStrategy) {
         this.store = new Object[initialCapacity];
         this.probingStrategy = probingStrategy;
     }
 
+    public OpenAddressingHashTable(int initialCapacity)
+    {
+        this(initialCapacity, new LinearProbing());
+    }
+
     public Optional<V> get(K key) {
         int trial = 0;
         int baseIndex = calcIndex(key, store.length);
@@ -75,7 +81,8 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
             {
                 if (!resize)
                 {
-                    addLink(nEntry);
+                    linkNewEntry(nEntry);
+                    size++;
                 }
 
                 store[index] = nEntry;
@@ -83,6 +90,9 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
             }
             else if (entry.key.equals(nEntry.key))
             {
+                if (!resize) {
+                    linkUpdatedEntry(entry);
+                }
                 entry.val = nEntry.val;
                 return true;
             }
@@ -91,7 +101,7 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
         return false;
     }
 
-    private void addLink(Entry<K, V> nEntry)
+    private void linkNewEntry(Entry<K, V> nEntry)
     {
         if (head == null)
         {
@@ -105,6 +115,28 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
         tail = nEntry;
     }
 
+    private void linkUpdatedEntry(Entry<K, V> entry)
+    {
+        if (head == null)
+        {
+            head = entry;
+        } else if (entry == head) {
+            if (entry.next != null) {
+                head = entry.next;
+                tail.next = entry;
+                entry.prev = tail;
+                tail = entry;
+            }
+        } else if (entry != tail) {
+            entry.prev.next = entry.next;
+            entry.next.prev = entry.prev;
+            tail.next = entry;
+            entry.prev = tail;
+            entry.next = null;
+            tail = entry;
+        }
+    }
+
     public void remove(K key) {
         int trial = 0;
         int baseIndex = calcIndex(key, store.length);
@@ -118,15 +150,16 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
             }
             else if (entry.key.equals(key))
             {
-                removeLink(entry);
+                unlinkEntry(entry);
                 store[index] = REMOVED;
+                size--;
                 return;
             }
             trial++;
         }
     }
 
-    private void removeLink(Entry<K, V> entry)
+    private void unlinkEntry(Entry<K, V> entry)
     {
         if (head == entry) {
             head = entry.next;
@@ -142,6 +175,10 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
         }
     }
 
+    public int size() {
+        return size;
+    }
+
     private int calcIndex(K key, int size) {
         return key.hashCode() % size;
     }
@@ -183,10 +220,20 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
         private V val;
         private Entry<K, V> prev;
         private Entry<K, V> next;
+
         public Entry(K key, V val) {
             this.key = key;
             this.val = val;
         }
+
+        public K key()
+        {
+            return key;
+        }
+        public V val()
+        {
+            return val;
+        }
         public String toString() {
             return "<" + key + "," + val + ">";
         }
@@ -239,9 +286,11 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
         table.put("z", "zellman");
         table.put("w", "walker");
         System.out.println(table);
+        System.out.println(table.size());
 
         table.remove("x");
         table.remove("z");
+        System.out.println(table.size());
 
         System.out.println(table.get("a"));
         System.out.println(table.get("b"));
@@ -252,6 +301,11 @@ public class OpenAddressingHashTable<K, V> implements Iterable<OpenAddressingHas
         table.put("z", "zebra");
         System.out.println(table.get("z"));
         System.out.println(table);
+        System.out.println(table.size());
+
+        table.put("w", "wanted");
+        System.out.println(table);
+        System.out.println(table.size());
 
         System.out.println(table.get("A"));
         System.out.println(table.get("B"));