Re-translate the Japanese version (#1871)

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ja/codes/swift/chapter_backtracking/permutations_ii.swift

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+/**
+ * File: permutations_ii.swift
+ * Created Time: 2023-04-30
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* バックトラッキング：順列 II */
+func backtrack(state: inout [Int], choices: [Int], selected: inout [Bool], res: inout [[Int]]) {
+    // 状態の長さが要素数に等しければ、解を記録
+    if state.count == choices.count {
+        res.append(state)
+        return
+    }
+    // すべての選択肢を走査
+    var duplicated: Set<Int> = []
+    for (i, choice) in choices.enumerated() {
+        // 枝刈り：要素の重複選択を許可せず、同値要素の重複選択も許可しない
+        if !selected[i], !duplicated.contains(choice) {
+            // 試行: 選択を行い、状態を更新
+            duplicated.insert(choice) // 選択済みの要素値を記録
+            selected[i] = true
+            state.append(choice)
+            // 次の選択へ進む
+            backtrack(state: &state, choices: choices, selected: &selected, res: &res)
+            // バックトラック：選択を取り消し、前の状態に戻す
+            selected[i] = false
+            state.removeLast()
+        }
+    }
+}
+
+/* 全順列 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("入力配列 nums = \(nums)")
+        print("すべての順列 res = \(res)")
+    }
+}