https://leetcode.com/problems/lfu-cache/

interview_prep/algorithm/java/ide_handicapped/lfu_cache/fastest/LFUCache.java

@@ -0,0 +1,103 @@
+class LFUCache {
+    class Node {
+        int key;
+        int val;
+        int cnt = 1;
+        Node prev;
+        Node next;
+        Node(int key, int val) {
+            this.key = key;
+            this.val = val;
+        }
+    }
+    Node[] keys = new Node[100001];
+    Node[] cnts = new Node[200001];
+    Node tail;
+    int size = 0;
+    int capacity;
+
+    public LFUCache(int capacity) {
+        this.capacity = capacity;
+    }
+
+    void remove(Node node) {
+        Node prev = node.prev;
+        Node next = node.next;
+
+        if (prev != null)
+            prev.next = next;
+
+        if (next != null)
+            next.prev = prev;
+
+        keys[node.key] = null;
+        if (cnts[node.cnt] == node) {
+            if (next != null && next.cnt == node.cnt)
+                cnts[node.cnt] = next;
+            else
+                cnts[node.cnt] = null;
+        }
+
+        if (tail == node)
+            tail = prev;
+
+        node.prev = null;
+        node.next = null;
+    }
+
+    void insert(Node node, Node next) {
+        cnts[node.cnt] = node;
+        keys[node.key] = node;
+        if (next == null) {
+            if (tail != null)
+                tail.next = node;
+            node.prev = tail;
+            tail = node;
+        }
+        else {
+            if (next.prev != null)
+                next.prev.next = node;
+            node.prev = next.prev;
+            node.next = next;
+            next.prev = node;
+        }
+    }
+
+    void moveUp(Node node) {
+        Node next = cnts[node.cnt + 1] != null ? cnts[node.cnt + 1] : cnts[node.cnt];
+        if (next == node)
+            next = node.next;
+
+        remove(node);
+        node.cnt++;
+        insert(node, next);
+    }
+
+    public int get(int key) {
+        Node node = keys[key];
+
+        if (node == null)
+            return -1;
+
+        moveUp(node);
+
+        return node.val;
+    }
+
+    public void put(int key, int value) {
+        Node node = keys[key];
+        if (node == null) {
+            node = new Node(key, value);
+            if (size >= capacity)
+                remove(tail);
+            else
+                size++;
+
+            insert(node, cnts[1]);
+        }
+        else {
+            moveUp(node);
+            node.val = value;
+        }
+    }
+}