From a953eca2342b74be1255a3d1a9359b37a2044526 Mon Sep 17 00:00:00 2001
From: bqlin <bqlins@163.com>
Date: Mon, 13 Dec 2021 15:54:48 +0800
Subject: [PATCH] =?UTF-8?q?0047.=E5=85=A8=E6=8E=92=E5=88=97II=EF=BC=9A?=
 =?UTF-8?q?=E4=BC=98=E5=8C=96=E6=8E=92=E7=89=88=EF=BC=8C=E8=A1=A5=E5=85=85?=
 =?UTF-8?q?Swift=E7=89=88=E6=9C=AC?=
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---
 problems/0047.全排列II.md | 38 ++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/problems/0047.全排列II.md b/problems/0047.全排列II.md
index d5d1528b..167e4b76 100644
--- a/problems/0047.全排列II.md
+++ b/problems/0047.全排列II.md
@@ -97,14 +97,15 @@ public:
 
 大家发现，去重最为关键的代码为：
 
-```
+```cpp
 if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false) {
     continue;
 }
 ```
 
 **如果改成 `used[i - 1] == true`， 也是正确的!**，去重代码如下：
-```
+
+```cpp
 if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == true) {
     continue;
 }
@@ -131,13 +132,13 @@ if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == true) {
 ## 总结
 
 这道题其实还是用了我们之前讲过的去重思路，但有意思的是，去重的代码中，这么写：
-```
+```cpp
 if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false) {
     continue;
 }
 ```
 和这么写：
-```
+```cpp
 if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == true) {
     continue;
 }
@@ -291,7 +292,36 @@ var permuteUnique = function (nums) {
 
 ```
 
+### Swift
 
+```swift
+func permuteUnique(_ nums: [Int]) -> [[Int]] {
+    let nums = nums.sorted() // 先排序，以方便相邻元素去重
+    var result = [[Int]]()
+    var path = [Int]()
+    var used = [Bool](repeating: false, count: nums.count)
+    func backtracking() {
+        if path.count == nums.count {
+            result.append(path)
+            return
+        }
+
+        for i in 0 ..< nums.count {
+            // !used[i - 1]表示同一树层nums[i - 1]使用过，直接跳过，这一步很关键！
+            if i > 0, nums[i] == nums[i - 1], !used[i - 1] { continue }
+            if used[i] { continue }
+            used[i] = true
+            path.append(nums[i])
+            backtracking()
+            // 回溯
+            path.removeLast()
+            used[i] = false
+        }
+    }
+    backtracking()
+    return result
+}
+```
 
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>