feat: add swift implementation to lcci problem: No.08.08 (doocs#2694)

Author: klever34

lcci/08.08.Permutation II/README.md

@@ -219,6 +219,42 @@ var permutation = function (S) {
 };
 ```
 
+```swift
+class Solution {
+    private var n: Int = 0
+    private var cs: [Character] = []
+    private var ans: [String] = []
+    private var vis: [Bool] = []
+    private var t: String = ""
+
+    func permutation(_ S: String) -> [String] {
+        cs = Array(S)
+        n = cs.count
+        cs.sort()
+        vis = Array(repeating: false, count: n)
+        dfs(0)
+        return ans
+    }
+
+    private func dfs(_ i: Int) {
+        if i == n {
+            ans.append(t)
+            return
+        }
+        for j in 0..<n {
+            if vis[j] || (j > 0 && !vis[j - 1] && cs[j] == cs[j - 1]) {
+                continue
+            }
+            vis[j] = true
+            t.append(cs[j])
+            dfs(i + 1)
+            t.removeLast()
+            vis[j] = false
+        }
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/08.08.Permutation II/README_EN.md

@@ -225,6 +225,42 @@ var permutation = function (S) {
 };
 ```
 
+```swift
+class Solution {
+    private var n: Int = 0
+    private var cs: [Character] = []
+    private var ans: [String] = []
+    private var vis: [Bool] = []
+    private var t: String = ""
+
+    func permutation(_ S: String) -> [String] {
+        cs = Array(S)
+        n = cs.count
+        cs.sort()
+        vis = Array(repeating: false, count: n)
+        dfs(0)
+        return ans
+    }
+
+    private func dfs(_ i: Int) {
+        if i == n {
+            ans.append(t)
+            return
+        }
+        for j in 0..<n {
+            if vis[j] || (j > 0 && !vis[j - 1] && cs[j] == cs[j - 1]) {
+                continue
+            }
+            vis[j] = true
+            t.append(cs[j])
+            dfs(i + 1)
+            t.removeLast()
+            vis[j] = false
+        }
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/08.08.Permutation II/Solution.swift

@@ -0,0 +1,33 @@
+class Solution {
+    private var n: Int = 0
+    private var cs: [Character] = []
+    private var ans: [String] = []
+    private var vis: [Bool] = []
+    private var t: String = ""
+
+    func permutation(_ S: String) -> [String] {
+        cs = Array(S)
+        n = cs.count
+        cs.sort()
+        vis = Array(repeating: false, count: n)
+        dfs(0)
+        return ans
+    }
+
+    private func dfs(_ i: Int) {
+        if i == n {
+            ans.append(t)
+            return
+        }
+        for j in 0..<n {
+            if vis[j] || (j > 0 && !vis[j - 1] && cs[j] == cs[j - 1]) {
+                continue
+            }
+            vis[j] = true
+            t.append(cs[j])
+            dfs(i + 1)
+            t.removeLast()
+            vis[j] = false
+        }
+    }
+}