feat: add Swift codes for top_k article (#578)

codes/swift/chapter_heap/top_k.swift

@@ -0,0 +1,35 @@
+/**
+ * File: top_k.swift
+ * Created Time: 2023-07-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+import utils
+
+/* 基于堆查找数组中最大的 k 个元素 */
+func topKHeap(nums: [Int], k: Int) -> [Int] {
+    // 将数组的前 k 个元素入堆
+    var heap = Array(nums.prefix(k))
+    // 从第 k+1 个元素开始，保持堆的长度为 k
+    for i in stride(from: k, to: nums.count, by: 1) {
+        // 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.first! {
+            heap.removeFirst()
+            heap.insert(nums[i], at: 0)
+        }
+    }
+    return heap
+}
+
+@main
+enum TopK {
+    /* Driver Code */
+    static func main() {
+        let nums = [1, 7, 6, 3, 2]
+        let k = 3
+
+        let res = topKHeap(nums: nums, k: k)
+        print("最大的 \(k) 个元素为")
+        PrintUtil.printHeap(queue: res)
+    }
+}