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/java/chapter_heap/top_k.java

@@ -0,0 +1,39 @@
+/**
+ * File: top_k.java
+ * Created Time: 2023-06-12
+ * Author: Krahets (krahets@163.com)
+ */
+
+package chapter_heap;
+
+import utils.*;
+import java.util.*;
+
+public class top_k {
+    /* 基于堆查找数组中最大的 k 个元素 */
+    static Queue<Integer> topKHeap(int[] nums, int k) {
+        Queue<Integer> heap = new PriorityQueue<Integer>();
+        // 将数组的前 k 个元素入堆
+        for (int i = 0; i < k; i++) {
+            heap.add(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.length; 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.peek()) {
+                heap.poll();
+                heap.add(nums[i]);
+            }
+        }
+        return heap;
+    }
+
+    public static void main(String[] args) {
+        int[] nums = { 1, 7, 6, 3, 2 };
+        int k = 3;
+
+        Queue<Integer> res = topKHeap(nums, k);
+        System.out.println("最大的 " + k + " 个元素为");
+        PrintUtil.printHeap(res);
+    }
+}