java: add «432. All O`one Data Structure»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/all-oone-data-structure.java

@@ -0,0 +1,119 @@
+import java.util.HashMap;
+
+class AllOne {
+  private class Node {
+    int freq;
+    Node prev, next;
+    Set<String> keys = new HashSet<>();
+
+    Node(int freq) {
+      this.freq = freq;
+    }
+
+    Node(int freq, Node prev, Node next) {
+      this.freq = freq;
+
+      this.prev = prev;
+      prev.next = this;
+
+      this.next = next;
+      next.prev = this;
+    }
+
+    void link(Map<String, Node> map, String key) {
+      keys.add(key);
+      map.put(key, this);
+    }
+
+    void remove() {
+      var prev = this.prev;
+      var next = this.next;
+
+      prev.next = next;
+      next.prev = prev;
+    }
+  }
+
+  Node head, tail;
+  Map<String, Node> map = new HashMap<>();
+
+  public AllOne() {
+    head = new Node(0);
+    tail = new Node(0);
+
+    head.next = tail;
+    tail.prev = head;
+  }
+
+  public void inc(String key) {
+    if (!map.containsKey(key)) {
+      var first = head.next;
+      if (first != tail && first.freq <= 1) {
+        first.link(map, key);
+        return;
+      }
+
+      var newNode = new Node(1, head, first);
+      newNode.link(map, key);
+      return;
+    }
+
+    var node = map.get(key);
+    var freq = node.freq;
+    node.keys.remove(key);
+
+    var next = node.next;
+    if (next != tail && next.freq == freq + 1) {
+      next.link(map, key);
+    } else {
+      var newNode = new Node(freq + 1, node, next);
+      newNode.link(map, key);
+    }
+
+    if (node.keys.isEmpty()) {
+      node.remove();
+    }
+  }
+
+  public void dec(String key) {
+    if (!map.containsKey(key)) {
+      return;
+    }
+
+    var node = map.get(key);
+    var freq = node.freq;
+    node.keys.remove(key);
+
+    if (freq == 1) {
+      map.remove(key);
+    } else {
+      var prev = node.prev;
+      if (prev != head && prev.freq == freq - 1) {
+        prev.link(map, key);
+      } else {
+        var newNode = new Node(freq - 1, prev, node);
+        newNode.link(map, key);
+      }
+    }
+
+    if (node.keys.isEmpty()) {
+      node.remove();
+    }
+  }
+
+  public String getMaxKey() {
+    if (tail.prev == head) {
+      return "";
+    }
+
+    return tail.prev.keys.iterator().next();
+  }
+
+  public String getMinKey() {
+    if (head.next == tail) {
+      return "";
+    }
+
+    return head.next.keys.iterator().next();
+  }
+}