Update Top K Frequent Elements - Leetcode 347.js

Author: gahogg

Top K Frequent Elements - Leetcode 347/Top K Frequent Elements - Leetcode 347.js

@@ -1,3 +1,106 @@
+var topKFrequent = function(nums, k) {
+    const countMap = new Map();
+    for (const num of nums) {
+        countMap.set(num, (countMap.get(num) || 0) + 1);
+    }
+
+    const heap = new MinHeap();
+
+    for (const [num, freq] of countMap) {
+        if (heap.size() < k) {
+            heap.add([freq, num]);
+        } else {
+            heap.add([freq, num]);
+            heap.poll();
+        }
+    }
+
+    return heap.toArray().map(pair => pair[1]);
+};
+
+// Helper class for MinHeap
+class MinHeap {
+    constructor() {
+        this.heap = [];
+    }
+
+    size() {
+        return this.heap.length;
+    }
+
+    add(pair) {
+        this.heap.push(pair);
+        this.bubbleUp();
+    }
+
+    poll() {
+        const min = this.heap[0];
+        const end = this.heap.pop();
+        if (this.size() > 0) {
+            this.heap[0] = end;
+            this.bubbleDown();
+        }
+        return min;
+    }
+
+    bubbleUp() {
+        let idx = this.size() - 1;
+        const element = this.heap[idx];
+        while (idx > 0) {
+            let parentIdx = Math.floor((idx - 1) / 2);
+            let parent = this.heap[parentIdx];
+            if (element[0] >= parent[0]) break;
+            this.heap[idx] = parent;
+            idx = parentIdx;
+        }
+        this.heap[idx] = element;
+    }
+
+    bubbleDown() {
+        let idx = 0;
+        const length = this.size();
+        const element = this.heap[0];
+        while (true) {
+            let leftChildIdx = 2 * idx + 1;
+            let rightChildIdx = 2 * idx + 2;
+            let swap = null;
+
+            if (leftChildIdx < length) {
+                let leftChild = this.heap[leftChildIdx];
+                if (leftChild[0] < element[0]) {
+                    swap = leftChildIdx;
+                }
+            }
+
+            if (rightChildIdx < length) {
+                let rightChild = this.heap[rightChildIdx];
+                if ((swap === null && rightChild[0] < element[0]) ||
+                    (swap !== null && rightChild[0] < this.heap[swap][0])) {
+                    swap = rightChildIdx;
+                }
+            }
+
+            if (swap === null) break;
+            this.heap[idx] = this.heap[swap];
+            idx = swap;
+        }
+        this.heap[idx] = element;
+    }
+
+    toArray() {
+        return this.heap;
+    }
+}
+
+
+
+
+
+
+
+
+
+
 var topKFrequent = function(nums, k) {
     const count = new Map();
     for (const num of nums) {