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https://github.com/krahets/hello-algo.git
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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
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4 changed files with 158 additions and 0 deletions
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@ -65,6 +65,10 @@ let package = Package(
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.executable(name: "bucket_sort", targets: ["bucket_sort"]),
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.executable(name: "bucket_sort", targets: ["bucket_sort"]),
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.executable(name: "counting_sort", targets: ["counting_sort"]),
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.executable(name: "counting_sort", targets: ["counting_sort"]),
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.executable(name: "radix_sort", targets: ["radix_sort"]),
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.executable(name: "radix_sort", targets: ["radix_sort"]),
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// chapter_divide_and_conquer
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.executable(name: "binary_search_recur", targets: ["binary_search_recur"]),
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.executable(name: "build_tree", targets: ["build_tree"]),
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.executable(name: "hanota", targets: ["hanota"]),
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// chapter_backtracking
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// chapter_backtracking
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.executable(name: "preorder_traversal_i_compact", targets: ["preorder_traversal_i_compact"]),
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.executable(name: "preorder_traversal_i_compact", targets: ["preorder_traversal_i_compact"]),
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.executable(name: "preorder_traversal_ii_compact", targets: ["preorder_traversal_ii_compact"]),
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.executable(name: "preorder_traversal_ii_compact", targets: ["preorder_traversal_ii_compact"]),
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@ -155,6 +159,10 @@ let package = Package(
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.executableTarget(name: "bucket_sort", path: "chapter_sorting", sources: ["bucket_sort.swift"]),
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.executableTarget(name: "bucket_sort", path: "chapter_sorting", sources: ["bucket_sort.swift"]),
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.executableTarget(name: "counting_sort", path: "chapter_sorting", sources: ["counting_sort.swift"]),
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.executableTarget(name: "counting_sort", path: "chapter_sorting", sources: ["counting_sort.swift"]),
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.executableTarget(name: "radix_sort", path: "chapter_sorting", sources: ["radix_sort.swift"]),
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.executableTarget(name: "radix_sort", path: "chapter_sorting", sources: ["radix_sort.swift"]),
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// chapter_divide_and_conquer
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.executableTarget(name: "binary_search_recur", path: "chapter_divide_and_conquer", sources: ["binary_search_recur.swift"]),
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.executableTarget(name: "build_tree", dependencies: ["utils"], path: "chapter_divide_and_conquer", sources: ["build_tree.swift"]),
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.executableTarget(name: "hanota", path: "chapter_divide_and_conquer", sources: ["hanota.swift"]),
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// chapter_backtracking
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// chapter_backtracking
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.executableTarget(name: "preorder_traversal_i_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_i_compact.swift"]),
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.executableTarget(name: "preorder_traversal_i_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_i_compact.swift"]),
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.executableTarget(name: "preorder_traversal_ii_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_ii_compact.swift"]),
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.executableTarget(name: "preorder_traversal_ii_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_ii_compact.swift"]),
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@ -0,0 +1,45 @@
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/**
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* File: binary_search_recur.swift
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* Created Time: 2023-09-02
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 二分查找:问题 f(i, j) */
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func dfs(nums: [Int], target: Int, i: Int, j: Int) -> Int {
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// 若区间为空,代表无目标元素,则返回 -1
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if i > j {
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return -1
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}
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// 计算中点索引 m
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let m = (i + j) / 2
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if nums[m] < target {
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// 递归子问题 f(m+1, j)
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return dfs(nums: nums, target: target, i: m + 1, j: j)
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} else if nums[m] > target {
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// 递归子问题 f(i, m-1)
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return dfs(nums: nums, target: target, i: i, j: m - 1)
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} else {
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// 找到目标元素,返回其索引
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return m
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}
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}
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/* 二分查找 */
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func binarySearch(nums: [Int], target: Int) -> Int {
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let n = nums.count
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// 求解问题 f(0, n-1)
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return dfs(nums: nums, target: target, i: 0, j: n - 1)
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}
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@main
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enum BinarySearchRecur {
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/* Driver Code */
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static func main() {
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let target = 6
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let nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35]
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// 二分查找(双闭区间)
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let index = binarySearch(nums: nums, target: target)
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print("目标元素 6 的索引 = \(index)")
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}
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}
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47
codes/swift/chapter_divide_and_conquer/build_tree.swift
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47
codes/swift/chapter_divide_and_conquer/build_tree.swift
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@ -0,0 +1,47 @@
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/**
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* File: build_tree.swift
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* Created Time: 2023-09-02
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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import utils
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/* 构建二叉树:分治 */
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func dfs(preorder: [Int], inorder: [Int], hmap: [Int: Int], i: Int, l: Int, r: Int) -> TreeNode? {
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// 子树区间为空时终止
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if r - l < 0 {
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return nil
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}
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// 初始化根节点
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let root = TreeNode(x: preorder[i])
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// 查询 m ,从而划分左右子树
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let m = hmap[preorder[i]]!
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// 子问题:构建左子树
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root.left = dfs(preorder: preorder, inorder: inorder, hmap: hmap, i: i + 1, l: l, r: m - 1)
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// 子问题:构建右子树
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root.right = dfs(preorder: preorder, inorder: inorder, hmap: hmap, i: i + 1 + m - l, l: m + 1, r: r)
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// 返回根节点
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return root
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}
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/* 构建二叉树 */
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func buildTree(preorder: [Int], inorder: [Int]) -> TreeNode? {
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// 初始化哈希表,存储 inorder 元素到索引的映射
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let hmap = inorder.enumerated().reduce(into: [:]) { $0[$1.element] = $1.offset }
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return dfs(preorder: preorder, inorder: inorder, hmap: hmap, i: 0, l: 0, r: inorder.count - 1)
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}
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@main
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enum BuildTree {
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/* Driver Code */
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static func main() {
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let preorder = [3, 9, 2, 1, 7]
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let inorder = [9, 3, 1, 2, 7]
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print("前序遍历 = \(preorder)")
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print("中序遍历 = \(inorder)")
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let root = buildTree(preorder: preorder, inorder: inorder)
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print("构建的二叉树为:")
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PrintUtil.printTree(root: root)
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}
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}
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58
codes/swift/chapter_divide_and_conquer/hanota.swift
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58
codes/swift/chapter_divide_and_conquer/hanota.swift
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/**
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* File: hanota.swift
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* Created Time: 2023-09-02
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 移动一个圆盘 */
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func move(src: inout [Int], tar: inout [Int]) {
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// 从 src 顶部拿出一个圆盘
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let pan = src.popLast()!
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// 将圆盘放入 tar 顶部
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tar.append(pan)
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}
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/* 求解汉诺塔:问题 f(i) */
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func dfs(i: Int, src: inout [Int], buf: inout [Int], tar: inout [Int]) {
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// 若 src 只剩下一个圆盘,则直接将其移到 tar
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if i == 1 {
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move(src: &src, tar: &tar)
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return
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}
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// 子问题 f(i-1) :将 src 顶部 i-1 个圆盘借助 tar 移到 buf
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dfs(i: i - 1, src: &src, buf: &tar, tar: &buf)
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// 子问题 f(1) :将 src 剩余一个圆盘移到 tar
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move(src: &src, tar: &tar)
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// 子问题 f(i-1) :将 buf 顶部 i-1 个圆盘借助 src 移到 tar
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dfs(i: i - 1, src: &buf, buf: &src, tar: &tar)
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}
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/* 求解汉诺塔 */
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func solveHanota(A: inout [Int], B: inout [Int], C: inout [Int]) {
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let n = A.count
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// 列表尾部是柱子顶部
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// 将 src 顶部 n 个圆盘借助 B 移到 C
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dfs(i: n, src: &A, buf: &B, tar: &C)
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}
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@main
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enum Hanota {
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/* Driver Code */
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static func main() {
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// 列表尾部是柱子顶部
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var A = [5, 4, 3, 2, 1]
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var B: [Int] = []
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var C: [Int] = []
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print("初始状态下:")
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print("A = \(A)")
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print("B = \(B)")
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print("C = \(C)")
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solveHanota(A: &A, B: &B, C: &C)
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print("圆盘移动完成后:")
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print("A = \(A)")
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print("B = \(B)")
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print("C = \(C)")
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}
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}
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