added lfucache feature

src/main/java/com/gatomalvado/done/lfucache/Dll.java

@@ -0,0 +1,63 @@
+package com.gatomalvado.done.lfucache;
+
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@NoArgsConstructor
+@Data
+public class Dll {
+
+    private DllNode head;
+    private DllNode tail;
+    private int currSize;
+
+    public void addFront(DllNode node) {
+        if(head == null) {
+            head = node;
+            tail = node;
+            return;
+        }
+        node.setNext(head);
+        head.setPrev(node);
+        head = node;
+    }
+
+    public void removeNode(DllNode node) {
+        DllNode prev = node.getPrev();
+        DllNode next = node.getNext();
+        if(node == tail) {
+            // this is a tail node;
+            if(prev == null) {
+                // this is a head node too
+                head = null;
+                tail = null;
+            } else {
+                prev.setNext(null);
+                tail = prev;
+            }
+        } else if(node == head) {
+            // this is a head node;
+            if(next == null) {
+                // this is a tail node too;
+                head = null;
+                tail = null;
+            } else {
+                next.setPrev(null);
+                head = next;
+            }
+        } else {
+            if(prev != null) {
+                prev.setNext(next);
+            }
+            if(next != null) {
+                next.setPrev(prev);
+            }
+        }
+
+        node.setPrev(null);
+        node.setNext(null);
+        this.currSize--;
+
+    }
+
+}

src/main/java/com/gatomalvado/done/lfucache/DllNode.java

@@ -0,0 +1,34 @@
+package com.gatomalvado.done.lfucache;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Getter
+@Setter
+@AllArgsConstructor
+@NoArgsConstructor
+public class DllNode {
+
+    private String key;
+    private String value;
+    private int freq;
+    private DllNode next;
+    private DllNode prev;
+
+    public DllNode(String key, String value) {
+        this.key = key;
+        this.value = value;
+        this.freq = 1;
+    }
+
+    @Override
+    public String toString() {
+        return "Node: {" +
+            "key: '" + key + '\'' +
+            ", value: '" + value + '\'' +
+            ", freq: " + freq +
+            '}';
+    }
+}

src/main/java/com/gatomalvado/done/lfucache/LfuCache.java

@@ -0,0 +1,79 @@
+package com.gatomalvado.done.lfucache;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class LfuCache {
+
+    private int maxCap;
+    private Map<String, DllNode> storage;
+    private Map<Integer, Dll> keyToListMap;
+    private int minFreq;
+
+    public LfuCache(int maxCap) {
+        this.maxCap = maxCap;
+        storage = new HashMap<>();
+        this.keyToListMap = new HashMap<>();
+    }
+
+    public String get(String key) {
+        DllNode node = storage.get(key);
+        if (node == null) {
+            System.out.println("no value exists for the key: "+key);
+            return null;
+        }
+        updateKey(node);
+        return node.getValue();
+    }
+
+    public void put(String key, String value) {
+        if(keyToListMap.containsKey(key)) {
+            DllNode node = storage.get(key);
+            node.setValue(value);
+            updateKey(node);
+        } else {
+            if(this.storage.size() == this.maxCap) {
+                Dll minFreqList = this.keyToListMap.get(this.minFreq);
+                DllNode tailNode = minFreqList.getTail();
+                if(minFreqList != null) {
+                    minFreqList.removeNode(tailNode);
+                }
+                if(minFreqList.getCurrSize() == 0) {
+                    this.keyToListMap.remove(this.minFreq);
+                }
+                this.storage.remove(tailNode.getKey());
+            }
+
+            DllNode newNode = new DllNode(key, value);
+            storage.put(key, newNode);
+            this.minFreq = 1;
+            Dll newList = this.keyToListMap.get(this.minFreq);
+            if(newList == null) {
+                newList = new Dll();
+            }
+            newList.addFront(newNode);
+            this.keyToListMap.put(this.minFreq, newList);
+        }
+    }
+
+    public void updateKey(DllNode node) {
+        int currFreq = node.getFreq();
+        node.setFreq(currFreq + 1);
+        Dll prevList = keyToListMap.get(currFreq);
+        prevList.removeNode(node);
+        Dll newList = keyToListMap.get(node.getFreq());
+        if(newList == null) {
+            newList = new Dll();
+        }
+        newList.addFront(node);
+        keyToListMap.put(node.getFreq(), newList);
+        if(prevList.getCurrSize() == 0) {
+            keyToListMap.remove(currFreq);
+            this.minFreq = node.getFreq();
+        }
+    }
+
+    public void printCache() {
+        System.out.println(storage);
+    }
+}

src/main/java/com/gatomalvado/done/lfucache/Main.java

@@ -0,0 +1,34 @@
+package com.gatomalvado.done.lfucache;
+
+public class Main {
+
+    public static void main(String[] args) {
+        LfuCache lfuCache = new LfuCache(4);
+        lfuCache.put("k1", "5");
+        lfuCache.printCache();
+        lfuCache.put("k2", "1");
+        lfuCache.printCache();
+        lfuCache.put("k3", "2");
+        lfuCache.printCache();
+        lfuCache.put("k4", "4");
+        lfuCache.printCache();
+        lfuCache.put("k5", "8");
+        lfuCache.printCache();
+        lfuCache.get("k1");
+        lfuCache.printCache();
+        lfuCache.put("k4", "8");
+        lfuCache.printCache();
+        lfuCache.put("k9", "8");
+        lfuCache.printCache();
+        lfuCache.put("k10", "8");
+        lfuCache.printCache();
+        lfuCache.get("k2");
+        lfuCache.printCache();
+        lfuCache.get("k3");
+        lfuCache.printCache();
+        lfuCache.get("k4");
+        lfuCache.printCache();
+        lfuCache.get("k1");
+        lfuCache.printCache();
+    }
+}