feat: add Swift codes for permutations_problem article (#482)

codes/swift/Package.swift

@@ -59,6 +59,8 @@ let package = Package(
         .executable(name: "preorder_traversal_ii_compact", targets: ["preorder_traversal_ii_compact"]),
         .executable(name: "preorder_traversal_iii_compact", targets: ["preorder_traversal_iii_compact"]),
         .executable(name: "preorder_traversal_iii_template", targets: ["preorder_traversal_iii_template"]),
+        .executable(name: "permutations_i", targets: ["permutations_i"]),
+        .executable(name: "permutations_ii", targets: ["permutations_ii"]),
     ],
     targets: [
         // helper
@@ -118,5 +120,7 @@ let package = Package(
         .executableTarget(name: "preorder_traversal_ii_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_ii_compact.swift"]),
         .executableTarget(name: "preorder_traversal_iii_compact", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_iii_compact.swift"]),
         .executableTarget(name: "preorder_traversal_iii_template", dependencies: ["utils"], path: "chapter_backtracking", sources: ["preorder_traversal_iii_template.swift"]),
+        .executableTarget(name: "permutations_i", path: "chapter_backtracking", sources: ["permutations_i.swift"]),
+        .executableTarget(name: "permutations_ii", path: "chapter_backtracking", sources: ["permutations_ii.swift"]),
     ]
 )

codes/swift/chapter_backtracking/permutations_i.swift

@@ -0,0 +1,50 @@
+/**
+ * File: permutations_i.swift
+ * Created Time: 2023-04-30
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 回溯算法：全排列 I */
+func backtrack(state: inout [Int], choices: [Int], selected: inout [Bool], res: inout [[Int]]) {
+    // 当状态长度等于元素数量时，记录解
+    if state.count == choices.count {
+        res.append(state)
+        return
+    }
+    // 遍历所有选择
+    for (i, choice) in choices.enumerated() {
+        // 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
+        if !selected[i] {
+            // 尝试：做出选择，更新状态
+            selected[i] = true
+            state.append(choice)
+            // 进行下一轮选择
+            backtrack(state: &state, choices: choices, selected: &selected, res: &res)
+            // 回退：撤销选择，恢复到之前的状态
+            selected[i] = false
+            state.removeLast()
+        }
+    }
+}
+
+/* 全排列 I */
+func permutationsI(nums: [Int]) -> [[Int]] {
+    var state: [Int] = []
+    var selected = Array(repeating: false, count: nums.count)
+    var res: [[Int]] = []
+    backtrack(state: &state, choices: nums, selected: &selected, res: &res)
+    return res
+}
+
+@main
+enum PermutationsI {
+    /* Driver Code */
+    static func main() {
+        let nums = [1, 2, 3]
+
+        let res = permutationsI(nums: nums)
+
+        print("输入数组 nums = \(nums)")
+        print("所有排列 res = \(res)")
+    }
+}

codes/swift/chapter_backtracking/permutations_ii.swift

@@ -0,0 +1,52 @@
+/**
+ * File: permutations_ii.swift
+ * Created Time: 2023-04-30
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 回溯算法：全排列 II */
+func backtrack(state: inout [Int], choices: [Int], selected: inout [Bool], res: inout [[Int]]) {
+    // 当状态长度等于元素数量时，记录解
+    if state.count == choices.count {
+        res.append(state)
+        return
+    }
+    // 遍历所有选择
+    var duplicated: Set<Int> = []
+    for (i, choice) in choices.enumerated() {
+        // 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
+        if !selected[i], !duplicated.contains(choice) {
+            // 尝试：做出选择，更新状态
+            duplicated.insert(choice) // 记录选择过的元素值
+            selected[i] = true
+            state.append(choice)
+            // 进行下一轮选择
+            backtrack(state: &state, choices: choices, selected: &selected, res: &res)
+            // 回退：撤销选择，恢复到之前的状态
+            selected[i] = false
+            state.removeLast()
+        }
+    }
+}
+
+/* 全排列 II */
+func permutationsII(nums: [Int]) -> [[Int]] {
+    var state: [Int] = []
+    var selected = Array(repeating: false, count: nums.count)
+    var res: [[Int]] = []
+    backtrack(state: &state, choices: nums, selected: &selected, res: &res)
+    return res
+}
+
+@main
+enum PermutationsII {
+    /* Driver Code */
+    static func main() {
+        let nums = [1, 2, 3]
+
+        let res = permutationsII(nums: nums)
+
+        print("输入数组 nums = \(nums)")
+        print("所有排列 res = \(res)")
+    }
+}