added max heap algorithm

whoisnp · abranhe · commit 351ccaaebc5e · 2020-10-15T00:42:19.000-04:00
diff --git a/algorithms/data-structures/maxHeap.js b/algorithms/data-structures/maxHeap.js
@@ -0,0 +1,77 @@
+class BinaryHeap {
+  constructor() {
+    this.heap = [];
+  }
+
+  insert(value) {
+    this.heap.push(value);
+    this.heapify();
+  }
+
+  size() {
+    return this.heap.length;
+  }
+
+  empty() {
+    return this.size() === 0;
+  }
+
+  heapify() {
+    let index = this.size() - 1;
+
+    while (index > 0) {
+      const element = this.heap[index];
+      const parentIndex = Math.floor((index - 1) / 2);
+      const parent = this.heap[parentIndex];
+
+      if (parent[0] >= element[0]) break;
+      this.heap[index] = parent;
+      this.heap[parentIndex] = element;
+      index = parentIndex;
+    }
+  }
+
+  extractMax() {
+    const max = this.heap[0];
+    const tmp = this.heap.pop();
+    if (!this.empty()) {
+      this.heap[0] = tmp;
+      this.sinkDown(0);
+    }
+    return max;
+  }
+
+  sinkDown(index) {
+    const left = 2 * index + 1;
+    const right = 2 * index + 2;
+    let largest = index;
+    const length = this.size();
+
+    if (left < length && this.heap[left][0] > this.heap[largest][0]) {
+      largest = left;
+    }
+    if (right < length && this.heap[right][0] > this.heap[largest][0]) {
+      largest = right;
+    }
+    // swap
+    if (largest !== index) {
+      const tmp = this.heap[largest];
+      this.heap[largest] = this.heap[index];
+      this.heap[index] = tmp;
+      this.sinkDown(largest);
+    }
+  }
+}
+
+const maxHeap = new BinaryHeap();
+maxHeap.insert([4]);
+maxHeap.insert([3]);
+maxHeap.insert([6]);
+maxHeap.insert([1]);
+maxHeap.insert([8]);
+maxHeap.insert([2]);
+
+while (!maxHeap.empty()) {
+  const mx = maxHeap.extractMax();
+  console.log(mx);
+}
