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/Package.swift

@@ -65,6 +65,10 @@ let package = Package(
         .executable(name: "bucket_sort", targets: ["bucket_sort"]),
         .executable(name: "counting_sort", targets: ["counting_sort"]),
         .executable(name: "radix_sort", targets: ["radix_sort"]),
+        // chapter_divide_and_conquer
+        .executable(name: "binary_search_recur", targets: ["binary_search_recur"]),
+        .executable(name: "build_tree", targets: ["build_tree"]),
+        .executable(name: "hanota", targets: ["hanota"]),
         // chapter_backtracking
         .executable(name: "preorder_traversal_i_compact", targets: ["preorder_traversal_i_compact"]),
         .executable(name: "preorder_traversal_ii_compact", targets: ["preorder_traversal_ii_compact"]),
@@ -155,6 +159,10 @@ let package = Package(
         .executableTarget(name: "bucket_sort", path: "chapter_sorting", sources: ["bucket_sort.swift"]),
         .executableTarget(name: "counting_sort", path: "chapter_sorting", sources: ["counting_sort.swift"]),
         .executableTarget(name: "radix_sort", path: "chapter_sorting", sources: ["radix_sort.swift"]),
+        // chapter_divide_and_conquer
+        .executableTarget(name: "binary_search_recur", path: "chapter_divide_and_conquer", sources: ["binary_search_recur.swift"]),
+        .executableTarget(name: "build_tree", dependencies: ["utils"], path: "chapter_divide_and_conquer", sources: ["build_tree.swift"]),
+        .executableTarget(name: "hanota", path: "chapter_divide_and_conquer", sources: ["hanota.swift"]),
         // chapter_backtracking
         .executableTarget(name: "preorder_traversal_i_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_i_compact.swift"]),
         .executableTarget(name: "preorder_traversal_ii_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_ii_compact.swift"]),

codes/swift/chapter_divide_and_conquer/binary_search_recur.swift

@@ -0,0 +1,45 @@
+/**
+ * File: binary_search_recur.swift
+ * Created Time: 2023-09-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 二分查找：问题 f(i, j) */
+func dfs(nums: [Int], target: Int, i: Int, j: Int) -> Int {
+    // 若区间为空，代表无目标元素，则返回 -1
+    if i > j {
+        return -1
+    }
+    // 计算中点索引 m
+    let m = (i + j) / 2
+    if nums[m] < target {
+        // 递归子问题 f(m+1, j)
+        return dfs(nums: nums, target: target, i: m + 1, j: j)
+    } else if nums[m] > target {
+        // 递归子问题 f(i, m-1)
+        return dfs(nums: nums, target: target, i: i, j: m - 1)
+    } else {
+        // 找到目标元素，返回其索引
+        return m
+    }
+}
+
+/* 二分查找 */
+func binarySearch(nums: [Int], target: Int) -> Int {
+    let n = nums.count
+    // 求解问题 f(0, n-1)
+    return dfs(nums: nums, target: target, i: 0, j: n - 1)
+}
+
+@main
+enum BinarySearchRecur {
+    /* Driver Code */
+    static func main() {
+        let target = 6
+        let nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35]
+
+        // 二分查找（双闭区间）
+        let index = binarySearch(nums: nums, target: target)
+        print("目标元素 6 的索引 = \(index)")
+    }
+}

codes/swift/chapter_divide_and_conquer/build_tree.swift

@@ -0,0 +1,47 @@
+/**
+ * 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)
+    }
+}

codes/swift/chapter_divide_and_conquer/hanota.swift

@@ -0,0 +1,58 @@
+/**
+ * File: hanota.swift
+ * Created Time: 2023-09-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 移动一个圆盘 */
+func move(src: inout [Int], tar: inout [Int]) {
+    // 从 src 顶部拿出一个圆盘
+    let pan = src.popLast()!
+    // 将圆盘放入 tar 顶部
+    tar.append(pan)
+}
+
+/* 求解汉诺塔：问题 f(i) */
+func dfs(i: Int, src: inout [Int], buf: inout [Int], tar: inout [Int]) {
+    // 若 src 只剩下一个圆盘，则直接将其移到 tar
+    if i == 1 {
+        move(src: &src, tar: &tar)
+        return
+    }
+    // 子问题 f(i-1) ：将 src 顶部 i-1 个圆盘借助 tar 移到 buf
+    dfs(i: i - 1, src: &src, buf: &tar, tar: &buf)
+    // 子问题 f(1) ：将 src 剩余一个圆盘移到 tar
+    move(src: &src, tar: &tar)
+    // 子问题 f(i-1) ：将 buf 顶部 i-1 个圆盘借助 src 移到 tar
+    dfs(i: i - 1, src: &buf, buf: &src, tar: &tar)
+}
+
+/* 求解汉诺塔 */
+func solveHanota(A: inout [Int], B: inout [Int], C: inout [Int]) {
+    let n = A.count
+    // 列表尾部是柱子顶部
+    // 将 src 顶部 n 个圆盘借助 B 移到 C
+    dfs(i: n, src: &A, buf: &B, tar: &C)
+}
+
+@main
+enum Hanota {
+    /* Driver Code */
+    static func main() {
+        // 列表尾部是柱子顶部
+        var A = [5, 4, 3, 2, 1]
+        var B: [Int] = []
+        var C: [Int] = []
+        print("初始状态下：")
+        print("A = \(A)")
+        print("B = \(B)")
+        print("C = \(C)")
+
+        solveHanota(A: &A, B: &B, C: &C)
+
+        print("圆盘移动完成后：")
+        print("A = \(A)")
+        print("B = \(B)")
+        print("C = \(C)")
+    }
+}