feat: Add the section of Top-K problem (#551)

* Add the section of Top-K problem

* Update my_heap.py

* Update build_heap.md

* Update my_heap.py

codes/cpp/chapter_heap/top_k.cpp

@@ -0,0 +1,37 @@
+/**
+ * File: top_k.cpp
+ * Created Time: 2023-06-12
+ * Author: Krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* 基于堆查找数组中最大的 k 个元素 */
+priority_queue<int, vector<int>, greater<int>> topKHeap(vector<int> &nums, int k) {
+    priority_queue<int, vector<int>, greater<int>> heap;
+    // 将数组的前 k 个元素入堆
+    for (int i = 0; i < k; i++) {
+        heap.push(nums[i]);
+    }
+    // 从第 k+1 个元素开始，保持堆的长度为 k
+    for (int i = k; i < nums.size(); 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] > heap.top()) {
+            heap.pop();
+            heap.push(nums[i]);
+        }
+    }
+    return heap;
+}
+
+// Driver Code
+int main() {
+    vector<int> nums = {1, 7, 6, 3, 2};
+    int k = 3;
+
+    priority_queue<int, vector<int>, greater<int>> res = topKHeap(nums, k);
+    cout << "最大的 " << k << " 个元素为: ";
+    printHeap(res);
+
+    return 0;
+}