feat: add Swift codes for chapter_searching articles (#309)

* feat: add Swift codes for linear_search article

* feat: add Swift codes for binary_search article

* feat: add Swift codes for hashing_search article

codes/swift/chapter_searching/linear_search.swift

@@ -0,0 +1,53 @@
+/**
+ * File: linear_search.swift
+ * Created Time: 2023-01-28
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+import utils
+
+/* 线性查找（数组） */
+func linearSearch(nums: [Int], target: Int) -> Int {
+    // 遍历数组
+    for i in nums.indices {
+        // 找到目标元素，返回其索引
+        if nums[i] == target {
+            return i
+        }
+    }
+    // 未找到目标元素，返回 -1
+    return -1
+}
+
+/* 线性查找（链表） */
+func linearSearch(head: ListNode?, target: Int) -> ListNode? {
+    var head = head
+    // 遍历链表
+    while head != nil {
+        // 找到目标结点，返回之
+        if head?.val == target {
+            return head
+        }
+        head = head?.next
+    }
+    // 未找到目标结点，返回 null
+    return nil
+}
+
+@main
+enum LinearSearch {
+    /* Driver Code */
+    static func main() {
+        let target = 3
+
+        /* 在数组中执行线性查找 */
+        let nums = [1, 5, 3, 2, 4, 7, 5, 9, 10, 8]
+        let index = linearSearch(nums: nums, target: target)
+        print("目标元素 3 的索引 = \(index)")
+
+        /* 在链表中执行线性查找 */
+        let head = ListNode.arrToLinkedList(arr: nums)
+        let node = linearSearch(head: head, target: target)
+        print("目标结点值 3 的对应结点对象为 \(node!)")
+    }
+}