Solve 2024-16 (part 1)

utils/queue.ts

@@ -0,0 +1,78 @@
+export class PriorityQueue<T> {
+  private readonly values: { node: T; priority: number }[] = [];
+
+  enqueue(node: T, priority: number) {
+    this.values.push({ node, priority });
+    this._bubbleUp();
+  }
+
+  dequeue() {
+    if (this.values.length === 0) return null;
+
+    const min = this.values[0];
+    const end = this.values.pop();
+
+    if (this.values.length > 0) {
+      this.values[0] = end!;
+      this._sinkDown();
+    }
+
+    return min;
+  }
+
+  size() {
+    return this.values.length;
+  }
+
+  _bubbleUp() {
+    let idx = this.values.length - 1;
+    const element = this.values[idx];
+
+    while (idx > 0) {
+      const parentIdx = Math.floor((idx - 1) / 2);
+      const parent = this.values[parentIdx];
+
+      if (element.priority >= parent.priority) break;
+
+      this.values[parentIdx] = element;
+      this.values[idx] = parent;
+      idx = parentIdx;
+    }
+  }
+
+  _sinkDown() {
+    let idx = 0;
+    const length = this.values.length;
+    const element = this.values[0];
+
+    while (true) {
+      const leftChildIdx = 2 * idx + 1;
+      const rightChildIdx = 2 * idx + 2;
+      let leftChild, rightChild;
+      let swap = null;
+
+      if (leftChildIdx < length) {
+        leftChild = this.values[leftChildIdx];
+        if (leftChild.priority < element.priority) {
+          swap = leftChildIdx;
+        }
+      }
+
+      if (rightChildIdx < length) {
+        rightChild = this.values[rightChildIdx];
+        if (
+          (swap === null && rightChild.priority < element.priority) ||
+          (swap !== null && rightChild.priority < leftChild!.priority)
+        ) {
+          swap = rightChildIdx;
+        }
+      }
+
+      if (swap === null) break;
+
+      this.values[idx] = this.values[swap];
+      this.values[swap] = element;
+      idx = swap;
+    }
+  }
+}