/** Decreases key by index
* Have amortized time of O(1)
*/
void decrease_key(int index, ScalarType& key)
{
fibonacci_heap_node* parent;
if(index >= max_num_nodes || index < 0)
return;
if(nodes[index]->index == -1)
return; // node is empty
if(key > nodes[index]->key)
return;
nodes[index]->key = key;
parent = nodes[index]->parent;
if(parent != NULL && nodes[index]->key < parent->key)
{
cut(nodes[index], parent);
cascading_cut(parent);
}
if(nodes[index]->key < min_root->key)
min_root = nodes[index];
}
void FibHeap<Key, Data, Compare>::cascading_cut(Node* child) noexcept{
Node* parent = child->parent;
if (parent!=nullptr){
if (child->mark==false)
child->mark = true;
else{
cut(child, parent);
cascading_cut(parent);
}
}
}
/**
* It does recursive cuts while there is a parent with a mark = true
* Cost: O(log n)
* Pre: node x to cut upwards
**/
void fib_heap::cascading_cut(node_t* x)
{
node_t* parent_x = x->parent;
if (parent_x != nullptr) {
if (x->mark == false)
x->mark = true;
else {
cut(x);
cascading_cut(parent_x);
}
}
}
/**
* Switching key of elem, pointed by pos, in new_key
* Cost: Worst case: O (log n); amortized: O(1)
* Pre: @pos is pointing to the elem whose key wants to be changed
* Post: fib_heap where elem now has the new_key value
**/
void fib_heap::decreaseKey( node_t* pos, int new_key)
{
if (new_key >= pos->key)
return; //DO NOTHING
else {
pos->key = new_key;
node_t *pos_parent = pos->parent;
if (pos_parent != nullptr && new_key < pos_parent->key) {
cut(pos);
cascading_cut(pos_parent);
}
if (pos->key < min->key)
min = pos;
}
}
void FibHeap<Key, Data, Compare>::decrease_key(Node* node, Key new_key) {
if (node == nullptr)
throw logic_error("There is no node to decrease key.");
if (Compare()(node->key, new_key))
return;
node->key = new_key;
Node* parent = node->parent;
if (parent==nullptr){
if (Compare()(node->key, root->key))
root = node;
}else{
if (Compare()(node->key, parent->key)){
cut(node, parent);
cascading_cut(parent);
}
}
}
static void cascading_cut(fibonacci_heap* heap, heap_node* y)
{
heap_node* z = y->parent;
if (z)
{
if (y->marked)
{
cut(heap, y, z);
cascading_cut(heap, z);
}
else
{
y->marked = true;
}
}
}
void cascading_cut(fibonacci_heap_node* tree)
{
fibonacci_heap_node *temp;
temp = tree->parent;
if(temp != NULL)
{
if(!tree->marked)
{
tree->marked = true;
}
else
{
cut(tree, temp);
cascading_cut(temp);
}
}
}
bool fibonacci_heap_decrease_key(fibonacci_heap* heap,
void* element,
void* priority)
{
heap_node* x;
heap_node* y;
if (!heap)
{
return false;
}
x = unordered_map_get(heap->node_map, element);
if (!x)
{
return false;
}
if (heap->key_compare_function(x->priority, priority) <= 0)
{
/* Cannot improve priority of the input element. */
return false;
}
x->priority = priority;
y = x->parent;
if (y && heap->key_compare_function(x->priority, y->priority) < 0)
{
cut(heap, x, y);
cascading_cut(heap, y);
}
if (heap->key_compare_function(x->priority, heap->minimum_node->priority) < 0)
{
heap->minimum_node = x;
}
return true;
}
