feat: add top_k.c and refactor top_k.js (#889)

* Add top_k.c based on my_heap.c

* Improve the implementation of top_k.js

* Add a comment to top_k

codes/c/chapter_heap/CMakeLists.txt

@@ -1,2 +1,2 @@
-add_executable(my_heap my_heap.c)
-
+add_executable(my_heap_test my_heap_test.c)
+add_executable(top_k top_k.c)

codes/c/chapter_heap/my_heap.c

@@ -34,6 +34,12 @@ MaxHeap *newMaxHeap(int nums[], int size) {
     return h;
 }
 
+/* 析构函数 */
+void freeMaxHeap(MaxHeap *h) {
+    // 释放内存
+    free(h);
+}
+
 /* 获取左子节点索引 */
 int left(MaxHeap *h, int i) {
     return 2 * i + 1;
@@ -144,37 +150,3 @@ void siftUp(MaxHeap *h, int i) {
         i = p;
     }
 }
-
-/* Driver Code */
-int main() {
-    /* 初始化堆 */
-    // 初始化大顶堆
-    int nums[] = {9, 8, 6, 6, 7, 5, 2, 1, 4, 3, 6, 2};
-    MaxHeap *heap = newMaxHeap(nums, sizeof(nums) / sizeof(int));
-    printf("输入数组并建堆后\n");
-    printHeap(heap->data, heap->size);
-
-    /* 获取堆顶元素 */
-    printf("\n堆顶元素为 %d\n", peek(heap));
-
-    /* 元素入堆 */
-    push(heap, 7);
-    printf("\n元素 7 入堆后\n");
-    printHeap(heap->data, heap->size);
-
-    /* 堆顶元素出堆 */
-    int top = pop(heap);
-    printf("\n堆顶元素 %d 出堆后\n", top);
-    printHeap(heap->data, heap->size);
-
-    /* 获取堆大小 */
-    printf("\n堆元素数量为 %d\n", size(heap));
-
-    /* 判断堆是否为空 */
-    printf("\n堆是否为空 %d\n", isEmpty(heap));
-
-    // 释放内存
-    free(heap);
-
-    return 0;
-}

codes/c/chapter_heap/my_heap_test.c

@@ -0,0 +1,41 @@
+/**
+ * File: my_heap_test.c
+ * Created Time: 2023-01-15
+ * Author: Reanon (793584285@qq.com)
+ */
+
+#include "my_heap.c"
+
+/* Driver Code */
+int main() {
+    /* 初始化堆 */
+    // 初始化大顶堆
+    int nums[] = {9, 8, 6, 6, 7, 5, 2, 1, 4, 3, 6, 2};
+    MaxHeap *heap = newMaxHeap(nums, sizeof(nums) / sizeof(int));
+    printf("输入数组并建堆后\n");
+    printHeap(heap->data, heap->size);
+
+    /* 获取堆顶元素 */
+    printf("\n堆顶元素为 %d\n", peek(heap));
+
+    /* 元素入堆 */
+    push(heap, 7);
+    printf("\n元素 7 入堆后\n");
+    printHeap(heap->data, heap->size);
+
+    /* 堆顶元素出堆 */
+    int top = pop(heap);
+    printf("\n堆顶元素 %d 出堆后\n", top);
+    printHeap(heap->data, heap->size);
+
+    /* 获取堆大小 */
+    printf("\n堆元素数量为 %d\n", size(heap));
+
+    /* 判断堆是否为空 */
+    printf("\n堆是否为空 %d\n", isEmpty(heap));
+
+    // 释放内存
+    freeMaxHeap(heap);
+
+    return 0;
+}

codes/c/chapter_heap/top_k.c

@@ -0,0 +1,73 @@
+/**
+ * File: top_k.c
+ * Created Time: 2023-10-26
+ * Author: Krahets (krahets163.com)
+ */
+
+#include "my_heap.c"
+
+/* 元素入堆 */
+void pushMinHeap(MaxHeap *maxHeap, int val) {
+    // 元素取反
+    push(maxHeap, -val);
+}
+
+/* 元素出堆 */
+int popMinHeap(MaxHeap *maxHeap) {
+    // 元素取反
+    return -pop(maxHeap);
+}
+
+/* 访问堆顶元素 */
+int peekMinHeap(MaxHeap *maxHeap) {
+    // 元素取反
+    return -peek(maxHeap);
+}
+
+/* 取出堆中元素 */
+int *getMinHeap(MaxHeap *maxHeap) {
+    // 将堆中所有元素取反并存入 res 数组
+    int *res = (int *)malloc(maxHeap->size * sizeof(int));
+    for (int i = 0; i < maxHeap->size; i++) {
+        res[i] = -maxHeap->data[i];
+    }
+    return res;
+}
+
+// 基于堆查找数组中最大的 k 个元素的函数
+int *topKHeap(int *nums, int sizeNums, int k) {
+    // 初始化小顶堆
+    // 请注意：我们将堆中所有元素取反，从而用大顶堆来模拟小顶堆
+    int empty[0];
+    MaxHeap *maxHeap = newMaxHeap(empty, 0);
+    // 将数组的前 k 个元素入堆
+    for (int i = 0; i < k; i++) {
+        pushMinHeap(maxHeap, nums[i]);
+    }
+    // 从第 k+1 个元素开始，保持堆的长度为 k
+    for (int i = k; i < sizeNums; i++) {
+        // 若当前元素大于堆顶元素，则将堆顶元素出堆、当前元素入堆
+        if (nums[i] > peekMinHeap(maxHeap)) {
+            popMinHeap(maxHeap);
+            pushMinHeap(maxHeap, nums[i]);
+        }
+    }
+    int *res = getMinHeap(maxHeap);
+    // 释放内存
+    freeMaxHeap(maxHeap);
+    return res;
+}
+
+/* Driver Code */
+int main() {
+    int nums[] = {1, 7, 6, 3, 2};
+    int k = 3;
+    int sizeNums = sizeof(nums) / sizeof(nums[0]);
+
+    int *res = topKHeap(nums, sizeNums, k);
+    printf("最大的 %d 个元素为: ", k);
+    printArray(res, k);
+
+    free(res);
+    return 0;
+}