Add JavaScript and TypeScript code of top_k and update some code style (#686)

* Update JS and TS code style

* Add JavaScript and TypeScript code of top_k

* Update top_k.ts

* Apply suggestions from code review

Co-authored-by: Justin Tse <xiefahit@gmail.com>

* Apply suggestions from code review

Co-authored-by: Justin Tse <xiefahit@gmail.com>

---------

Co-authored-by: Yudong Jin <krahets@163.com>

codes/typescript/chapter_array_and_linkedlist/array.ts

@@ -53,7 +53,7 @@ function traverse(nums: number[]): void {
         count++;
     }
     // 直接遍历数组
-    for (let num of nums) {
+    for (const num of nums) {
         count += 1;
     }
 }
@@ -98,4 +98,4 @@ traverse(nums);
 let index = find(nums, 3);
 console.log('在 nums 中查找元素 3 ，得到索引 =', index);
 
-export {};
+export { };

codes/typescript/chapter_dynamic_programming/climbing_stairs_backtrack.ts

@@ -14,7 +14,7 @@ function backtrack(
     // 当爬到第 n 阶时，方案数量加 1
     if (state === n) res.set(0, res.get(0) + 1);
     // 遍历所有选择
-    for (let choice of choices) {
+    for (const choice of choices) {
         // 剪枝：不允许越过第 n 阶
         if (state + choice > n) break;
         // 尝试：做出选择，更新状态
@@ -38,4 +38,4 @@ const n = 9;
 const res = climbingStairsBacktrack(n);
 console.log(`爬 ${n} 阶楼梯共有 ${res} 种方案`);
 
-export {};
+export { };

codes/typescript/chapter_graph/graph_adjacency_list.ts

@@ -70,7 +70,7 @@ class GraphAdjList {
         // 在邻接表中删除顶点 vet 对应的链表
         this.adjList.delete(vet);
         // 遍历其他顶点的链表，删除所有包含 vet 的边
-        for (let set of this.adjList.values()) {
+        for (const set of this.adjList.values()) {
             const index: number = set.indexOf(vet);
             if (index > -1) {
                 set.splice(index, 1);

codes/typescript/chapter_heap/my_heap.ts

@@ -114,6 +114,11 @@ class MaxHeap {
     public print(): void {
         printHeap(this.maxHeap);
     }
+
+    /* 取出堆中元素 */
+    public getMaxHeap(): number[] {
+        return this.maxHeap;
+    }
 }
 
 /* Driver Code */
@@ -144,3 +149,5 @@ console.log(`\n堆元素数量为 ${size}`);
 /* 判断堆是否为空 */
 const isEmpty = maxHeap.isEmpty();
 console.log(`\n堆是否为空 ${isEmpty}`);
+
+export { MaxHeap };

codes/typescript/chapter_heap/top_k.ts

@@ -0,0 +1,34 @@
+/**
+ * File: top_k.ts
+ * Created Time: 2023-08-13
+ * Author: Justin (xiefahit@gmail.com)
+ */
+
+import { MaxHeap } from './my_heap';
+
+/* 基于堆查找数组中最大的 k 个元素 */
+function top_k_heap(nums: number[], k: number): number[] {
+    // 将堆中所有元素取反，从而用大顶堆来模拟小顶堆
+    const invertedNums = nums.map(num => -num);
+    // 将数组的前 k 个元素入堆
+    const heap = new MaxHeap(invertedNums.slice(0, k));
+    // 从第 k+1 个元素开始，保持堆的长度为 k
+    for (let i = k; i < invertedNums.length; i++) {
+        // 若当前元素小于堆顶元素，则将堆顶元素出堆、当前元素入堆
+        if (invertedNums[i] < heap.peek()) {
+            heap.pop();
+            heap.push(invertedNums[i]);
+        }
+    }
+    // 取出堆中元素
+    const maxHeap = heap.getMaxHeap();
+    // 对堆中元素取相反数
+    const invertedMaxHeap = maxHeap.map(num => -num);
+    return invertedMaxHeap;
+}
+
+/* Driver Code */
+const nums = [1, 7, 6, 3, 2];
+const k = 3;
+const res = top_k_heap(nums, k);
+console.log(`最大的 ${k} 个元素为`, res);