Merge 144030aed1 into f3f32ae3ca

data_structures/heap/fibonacci_heap.py

@@ -0,0 +1,178 @@
+import math
+
+
+class FibonacciHeapNode:
+    def __init__(self, key, value=None):
+        self.key = key
+        self.value = value
+        self.degree = 0
+        self.parent = None
+        self.child = None
+        self.mark = False
+        self.next = self
+        self.prev = self
+
+    def add_child(self, node):
+        if not self.child:
+            self.child = node
+        else:
+            node.prev = self.child
+            node.next = self.child.next
+            self.child.next.prev = node
+            self.child.next = node
+        node.parent = self
+        self.degree += 1
+
+    def remove_child(self, node):
+        if node.next == node:  # Single child
+            self.child = None
+        elif self.child == node:
+            self.child = node.next
+        node.prev.next = node.next
+        node.next.prev = node.prev
+        node.parent = None
+        self.degree -= 1
+
+
+class FibonacciHeap:
+    def __init__(self):
+        self.min_node = None
+        self.total_nodes = 0
+
+    def is_empty(self):
+        return self.min_node is None
+
+    def insert(self, key, value=None):
+        node = FibonacciHeapNode(key, value)
+        self._merge_with_root_list(node)
+        if not self.min_node or node.key < self.min_node.key:
+            self.min_node = node
+        self.total_nodes += 1
+        return node
+
+    def find_min(self):
+        return self.min_node
+
+    def union(self, other_heap):
+        if not other_heap.min_node:
+            return self
+        if not self.min_node:
+            self.min_node = other_heap.min_node
+        else:
+            self._merge_with_root_list(other_heap.min_node)
+            if other_heap.min_node.key < self.min_node.key:
+                self.min_node = other_heap.min_node
+        self.total_nodes += other_heap.total_nodes
+
+    def extract_min(self):
+        z = self.min_node
+        if z:
+            if z.child:
+                children = list(self._iterate(z.child))
+                for child in children:
+                    self._merge_with_root_list(child)
+                    child.parent = None
+            self._remove_from_root_list(z)
+            if z == z.next:
+                self.min_node = None
+            else:
+                self.min_node = z.next
+                self._consolidate()
+            self.total_nodes -= 1
+        return z
+
+    def decrease_key(self, x, new_key):
+        if new_key > x.key:
+            raise ValueError("New key is greater than current key")
+        x.key = new_key
+        y = x.parent
+        if y and x.key < y.key:
+            self._cut(x, y)
+            self._cascading_cut(y)
+        if x.key < self.min_node.key:
+            self.min_node = x
+
+    def delete(self, x):
+        self.decrease_key(x, -math.inf)
+        self.extract_min()
+
+    def _cut(self, x, y):
+        y.remove_child(x)
+        self._merge_with_root_list(x)
+        x.mark = False
+
+    def _cascading_cut(self, y):
+        if z := y.parent:
+            if not y.mark:
+                y.mark = True
+            else:
+                self._cut(y, z)
+                self._cascading_cut(z)
+
+    def _merge_with_root_list(self, node):
+        if not self.min_node:
+            self.min_node = node
+        else:
+            node.prev = self.min_node
+            node.next = self.min_node.next
+            self.min_node.next.prev = node
+            self.min_node.next = node
+
+    def _remove_from_root_list(self, node):
+        if node.next == node:
+            self.min_node = None
+        else:
+            node.prev.next = node.next
+            node.next.prev = node.prev
+
+    def _consolidate(self):
+        array_size = int(math.log(self.total_nodes) * 2) + 1
+        array = [None] * array_size
+        nodes = list(self._iterate(self.min_node))
+        for w in nodes:
+            x = w
+            d = x.degree
+            while array[d]:
+                y = array[d]
+                if x.key > y.key:
+                    x, y = y, x
+                self._link(y, x)
+                array[d] = None
+                d += 1
+            array[d] = x
+        self.min_node = None
+        for i in range(array_size):
+            if array[i]:
+                if not self.min_node:
+                    self.min_node = array[i]
+                else:
+                    self._merge_with_root_list(array[i])
+                    if array[i].key < self.min_node.key:
+                        self.min_node = array[i]
+
+    def _link(self, y, x):
+        self._remove_from_root_list(y)
+        x.add_child(y)
+        y.mark = False
+
+    def _iterate(self, start):
+        node = start
+        while True:
+            yield node
+            node = node.next
+            if node == start:
+                break
+
+
+# Example usage
+if __name__ == "__main__":
+    fh = FibonacciHeap()
+    n1 = fh.insert(10, "value1")
+    n2 = fh.insert(2, "value2")
+    n3 = fh.insert(15, "value3")
+
+    print("Min:", fh.find_min().key)  # Output: 2
+    fh.decrease_key(n3, 1)
+    print("Min after decrease key:", fh.find_min().key)  # Output: 1
+    fh.extract_min()
+    print("Min after extract:", fh.find_min().key)  # Output: 2