Optimize makeBlockTemplates

backend/src/utils/pairing-heap.ts

@@ -0,0 +1,174 @@
+export type HeapNode<T> = {
+  element: T
+  child?: HeapNode<T>
+  next?: HeapNode<T>
+  prev?: HeapNode<T>
+} | null | undefined;
+
+// minimal pairing heap priority queue implementation
+export class PairingHeap<T> {
+  private root: HeapNode<T> = null;
+  private comparator: (a: T, b: T) => boolean;
+
+  // comparator function should return 'true' if a is higher priority than b
+  constructor(comparator: (a: T, b: T) => boolean) {
+    this.comparator = comparator;
+  }
+
+  isEmpty(): boolean {
+    return !this.root;
+  }
+
+  add(element: T): HeapNode<T> {
+    const node: HeapNode<T> = {
+      element
+    };
+
+    this.root = this.meld(this.root, node);
+
+    return node;
+  }
+
+  // returns the top priority element without modifying the queue
+  peek(): T | void {
+    return this.root?.element;
+  }
+
+  // removes and returns the top priority element
+  pop(): T | void {
+    let element;
+    if (this.root) {
+      const node = this.root;
+      element = node.element;
+      this.root = this.mergePairs(node.child);
+    }
+    return element;
+  }
+
+  deleteNode(node: HeapNode<T>): void {
+    if (!node) {
+      return;
+    }
+
+    if (node === this.root) {
+      this.root = this.mergePairs(node.child);
+    }
+    else {
+      if (node.prev) {
+        if (node.prev.child === node) {
+          node.prev.child = node.next;
+        }
+        else {
+          node.prev.next = node.next;
+        }
+      }
+      if (node.next) {
+        node.next.prev = node.prev;
+      }
+      this.root = this.meld(this.root, this.mergePairs(node.child));
+    }
+
+    node.child = null;
+    node.prev = null;
+    node.next = null;
+  }
+
+  // fix the heap after increasing the priority of a given node
+  increasePriority(node: HeapNode<T>): void {
+    // already the top priority element
+    if (!node || node === this.root) {
+      return;
+    }
+    // extract from siblings
+    if (node.prev) {
+      if (node.prev?.child === node) {
+        if (this.comparator(node.prev.element, node.element)) {
+          // already in a valid position
+          return;
+        }
+        node.prev.child = node.next;
+      }
+      else {
+        node.prev.next = node.next;
+      }
+    }
+    if (node.next) {
+      node.next.prev = node.prev;
+    }
+
+    this.root = this.meld(this.root, node);
+  }
+
+  decreasePriority(node: HeapNode<T>): void {
+    this.deleteNode(node);
+    this.root = this.meld(this.root, node);
+  }
+
+  meld(a: HeapNode<T>, b: HeapNode<T>): HeapNode<T> {
+    if (!a) {
+      return b;
+    }
+    if (!b || a === b) {
+      return a;
+    }
+
+    let parent: HeapNode<T> = b;
+    let child: HeapNode<T> = a;
+    if (this.comparator(a.element, b.element)) {
+      parent = a;
+      child = b;
+    }
+
+    child.next = parent.child;
+    if (parent.child) {
+      parent.child.prev = child;
+    }
+    child.prev = parent;
+    parent.child = child;
+
+    parent.next = null;
+    parent.prev = null;
+
+    return parent;
+  }
+
+  mergePairs(node: HeapNode<T>): HeapNode<T> {
+    if (!node) {
+      return null;
+    }
+
+    let current: HeapNode<T> = node;
+    let next: HeapNode<T>;
+    let nextCurrent: HeapNode<T>;
+    let pairs: HeapNode<T>;
+    let melded: HeapNode<T>;
+    while (current) {
+      next = current.next;
+      if (next) {
+        nextCurrent = next.next;
+        melded = this.meld(current, next);
+        if (melded) {
+          melded.prev = pairs;
+        }
+        pairs = melded;
+      }
+      else {
+        nextCurrent = null;
+        current.prev = pairs;
+        pairs = current;
+        break;
+      }
+      current = nextCurrent;
+    }
+
+    melded = null;
+    let prev: HeapNode<T>;
+    while (pairs) {
+      prev = pairs.prev;
+      melded = this.meld(melded, pairs);
+      pairs = prev;
+    }
+
+    return melded;
+  }
+}