2021-01-26

public class FibonacciHeap {

private Node minNode;
private int size;

public FibonacciHeap() {
    minNode = null;
    size = 0;
}

private FibonacciHeap(Node node) {
    minNode = node;
    size = 1;
}

private FibonacciHeap(Node minNode, int size) {
    this.minNode = minNode;
    this.size = size;
}

public boolean isEmpty() {
    return minNode == null;
}

public void clear() {
    minNode = null;
    size = 0;
}

public Node insert(T key) {
    Node node = new Node(key);
    minNode = mergeLists(minNode, node);
    size++;
    return node;
}

public Node findMinimum() {
    return minNode;
}

public void decreaseKey(Node node, T newKey) {
    if (newKey.compareTo(node.key) > 0) {
        throw new IllegalArgumentException("New key is larger than old key.");
    }

    node.key = newKey;
    Node parent = node.parent;
    if (parent != null && node.compareTo(parent) < 0) {
        cut(node, parent);
        cascadingCut(parent);
    }
    if (node.compareTo(minNode) < 0) {
        minNode = node;
    }
}

private void cut(Node node, Node parent) {
    removeNodeFromList(node);
    parent.degree--;
    mergeLists(minNode, node);
    node.isMarked = false;
}

private void cascadingCut(Node node) {
    Node parent = node.parent;
    if (parent != null) {
        if (node.isMarked) {
            cut(node, parent);
            cascadingCut(parent);
        } else {
            node.isMarked = true;
        }
    }
}

public void delete(Node node) {
    // This is a special implementation of decreaseKey that sets the
    // argument to the minimum value. This is necessary to make generic keys
    // work, since there is no MIN_VALUE constant for generic types.
    node.isMinimum = true;
    Node parent = node.parent;
    if (parent != null) {
        cut(node, parent);
        cascadingCut(parent);
    }
    minNode = node;

    extractMin();
}

public Node extractMin() {
    Node extractedMin = minNode;
    if (extractedMin != null) {
        // Set parent to null for the minimum's children
        if (extractedMin.child != null) {
            Node child = extractedMin.child;
            do {
                child.parent = null;
                child = child.next;
            } while (child != extractedMin.child);
        }

        Node nextInRootList = minNode.next == minNode ? null : minNode.next;

        // Remove min from root list
        removeNodeFromList(extractedMin);
        size--;

        // Merge the children of the minimum node with the root list
        minNode = mergeLists(nextInRootList, extractedMin.child);

        if (nextInRootList != null) {
            minNode = nextInRootList;
            consolidate();
        }
    }
    return extractedMin;
}

private void consolidate() {
    List> aux = new ArrayList>();
    NodeListIterator it = new NodeListIterator(minNode);
    while (it.hasNext()) {
        Node current = it.next();

        while (aux.size() <= current.degree + 1) {
            aux.add(null);
        }

        // If there exists another node with the same degree, merge them
        while (aux.get(current.degree) != null) {
            if (current.key.compareTo(aux.get(current.degree).key) > 0) {
                Node temp = current;
                current = aux.get(current.degree);
                aux.set(current.degree, temp);
            }
            linkHeaps(aux.get(current.degree), current);
            aux.set(current.degree, null);
            current.degree++;
        }

        while (aux.size() <= current.degree + 1) {
            aux.add(null);
        }
        aux.set(current.degree, current);
    }

    minNode = null;
    for (int i = 0; i < aux.size(); i++) {
        if (aux.get(i) != null) {
            // Remove siblings before merging
            aux.get(i).next = aux.get(i);
            aux.get(i).prev = aux.get(i);
            minNode = mergeLists(minNode, aux.get(i));
        }
    }
}

private void removeNodeFromList(Node node) {
    Node prev = node.prev;
    Node next = node.next;
    prev.next = next;
    next.prev = prev;

    node.next = node;
    node.prev = node;
}

private void linkHeaps(Node max, Node min) {
    removeNodeFromList(max);
    min.child = mergeLists(max, min.child);
    max.parent = min;
    max.isMarked = false;
}

// Union another fibonacci heap with this one
public void union(FibonacciHeap other) {
    minNode = mergeLists(minNode, other.minNode);
    size += other.size;
}

// Merges two lists and returns the minimum node
public static > Node mergeLists(
        Node a, Node b) {

    if (a == null && b == null) {
        return null;
    }
    if (a == null) {
        return b;
    }
    if (b == null) {
        return a;
    }

    Node temp = a.next;
    a.next = b.next;
    a.next.prev = a;
    b.next = temp;
    b.next.prev = b;

    return a.compareTo(b) < 0 ? a : b;
}

public void print() {
    System.out.println("Fibonacci heap:");
    if (minNode != null) {
        minNode.print(0);
    }
}

public static class Node>
        implements Comparable> {

    private T key;
    private int degree;
    private Node parent;
    private Node child;
    private Node prev;
    private Node next;
    private boolean isMarked;
    private boolean isMinimum;

    public Node() {
        key = null;
    }

    public Node(T key) {
        this.key = key;
        next = this;
        prev = this;
    }

    public T getKey() {
        return key;
    }

    public int compareTo(Node other) {
        return this.key.compareTo(other.key);
    }

    private void print(int level) {
        Node curr = this;
        do {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < level; i++) {
                sb.append(" ");
            }
            sb.append(curr.key.toString());
            System.out.println(sb.toString());
            if (curr.child != null) {
                curr.child.print(level + 1);
            }
            curr = curr.next;
        } while (curr != this);
    }
}

// This Iterator is used to simplify the consolidate() method. It works by
// gathering a list of the nodes in the list in the constructor since the
// nodes can change during consolidation.
public static class NodeListIterator>
        implements Iterator> {

    private Queue> items = new LinkedList>();

    public NodeListIterator(Node start) {
        if (start == null) {
            return;
        }

        Node current = start;
        do {
            items.add(current);
            current = current.next;
        } while (start != current);
    }

    public boolean hasNext() {
        return items.peek() != null;
    }

    public Node next() {
        return items.poll();
    }

    public void remove() {
        throw new UnsupportedOperationException(
                "NodeListIterator.remove is not implemented");
    }
}

}