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/python/chapter_heap/my_heap.py

@@ -14,7 +14,7 @@ class MaxHeap:
     """大顶堆"""
 
     def __init__(self, nums: list[int]):
-        """构造方法"""
+        """构造方法，根据输入列表建堆"""
         # 将列表元素原封不动添加进堆
         self.max_heap = nums
         # 堆化除叶节点以外的其他所有节点

codes/python/chapter_heap/top_k.py

@@ -0,0 +1,37 @@
+"""
+File: top_k.py
+Created Time: 2023-06-10
+Author: Krahets (krahets@163.com)
+"""
+
+import sys, os.path as osp
+
+sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
+from modules import *
+
+import heapq
+
+
+def top_k_heap(nums: list[int], k: int) -> list[int]:
+    """基于堆查找数组中最大的 k 个元素"""
+    heap = []
+    # 将数组的前 k 个元素入堆
+    for i in range(k):
+        heapq.heappush(heap, nums[i])
+    # 从第 k+1 个元素开始，保持堆的长度为 k
+    for i in range(k, len(nums)):
+        # 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[0]:
+            heapq.heappop(heap)
+            heapq.heappush(heap, nums[i])
+    return heap
+
+
+"""Driver Code"""
+if __name__ == "__main__":
+    nums = [1, 7, 6, 3, 2]
+    k = 3
+
+    res = top_k_heap(nums, k)
+    print(f"最大的 {k} 个元素为")   
+    print_heap(res)