Feature/chapter divide and conquer swift (#719)

* feat: add Swift codes for binary_search_recur article

* feat: add Swift codes for build_binary_tree_problem article

* feat: add Swift codes for hanota_problem article

codes/swift/chapter_divide_and_conquer/build_tree.swift

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+/**
+ * File: build_tree.swift
+ * Created Time: 2023-09-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+import utils
+
+/* 构建二叉树：分治 */
+func dfs(preorder: [Int], inorder: [Int], hmap: [Int: Int], i: Int, l: Int, r: Int) -> TreeNode? {
+    // 子树区间为空时终止
+    if r - l < 0 {
+        return nil
+    }
+    // 初始化根节点
+    let root = TreeNode(x: preorder[i])
+    // 查询 m ，从而划分左右子树
+    let m = hmap[preorder[i]]!
+    // 子问题：构建左子树
+    root.left = dfs(preorder: preorder, inorder: inorder, hmap: hmap, i: i + 1, l: l, r: m - 1)
+    // 子问题：构建右子树
+    root.right = dfs(preorder: preorder, inorder: inorder, hmap: hmap, i: i + 1 + m - l, l: m + 1, r: r)
+    // 返回根节点
+    return root
+}
+
+/* 构建二叉树 */
+func buildTree(preorder: [Int], inorder: [Int]) -> TreeNode? {
+    // 初始化哈希表，存储 inorder 元素到索引的映射
+    let hmap = inorder.enumerated().reduce(into: [:]) { $0[$1.element] = $1.offset }
+    return dfs(preorder: preorder, inorder: inorder, hmap: hmap, i: 0, l: 0, r: inorder.count - 1)
+}
+
+@main
+enum BuildTree {
+    /* Driver Code */
+    static func main() {
+        let preorder = [3, 9, 2, 1, 7]
+        let inorder = [9, 3, 1, 2, 7]
+        print("前序遍历 = \(preorder)")
+        print("中序遍历 = \(inorder)")
+
+        let root = buildTree(preorder: preorder, inorder: inorder)
+        print("构建的二叉树为：")
+        PrintUtil.printTree(root: root)
+    }
+}