diff --git a/problems/0028.实现strStr.md b/problems/0028.实现strStr.md
index 91f8a524..cc73420b 100644
--- a/problems/0028.实现strStr.md
+++ b/problems/0028.实现strStr.md
@@ -894,7 +894,58 @@ var strStr = function (haystack, needle) {
 };
 ```
 
+Swift 版本
 
+> 前缀表统一减一
+
+```swift
+func strStr(_ haystack: String, _ needle: String) -> Int {
+    
+    let s = Array(haystack), p = Array(needle)
+    guard p.count != 0 else { return 0 }
+    
+    // 2 pointer
+    var j = -1
+    var next = [Int](repeating: -1, count: needle.count)
+    // KMP
+    getNext(&next, needle: p)
+    for i in 0 ..< s.count {
+        while j >= 0 && s[i] != p[j + 1] {
+            //不匹配之后寻找之前匹配的位置
+            j = next[j]
+        }
+        if s[i] == p[j + 1] {
+            //匹配，双指针同时后移
+            j += 1
+        }
+        if j == (p.count - 1) {
+            //出现匹配字符串
+            return i - p.count + 1
+        }
+    }
+    return -1
+}
+
+//前缀表统一减一
+func getNext(_ next: inout [Int], needle: [Character]) {
+    
+    var j: Int = -1
+    next[0] = j
+    
+    // i 从 1 开始
+    for i in 1 ..< needle.count {
+        while j >= 0 && needle[i] != needle[j + 1] {
+            j = next[j]
+        }
+        if needle[i] == needle[j + 1] {
+            j += 1;
+        }
+        next[i] = j
+    }
+    print(next)
+}
+
+```
 
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>
diff --git a/problems/0077.组合.md b/problems/0077.组合.md
index 6c74ab52..ef7031e3 100644
--- a/problems/0077.组合.md
+++ b/problems/0077.组合.md
@@ -405,7 +405,7 @@ class Solution:
             if len(path) == k:
                 res.append(path[:])
                 return
-            for i in range(StartIndex, n-(k-len(path)) + 2):
+            for i in range(StartIndex, n + 1):
                 path.append(i)
                 backtrack(n, k, i+1)
                 path.pop()
@@ -414,7 +414,7 @@ class Solution:
 ```
 
 剪枝：
-```python3
+```python
 class Solution:
     def combine(self, n: int, k: int) -> List[List[int]]:
         res=[]  #存放符合条件结果的集合
@@ -423,7 +423,7 @@ class Solution:
             if len(path) == k:
                 res.append(path[:])
             return 
-            for i in range(startIndex,n-(k-len(path))+2):  #优化的地方
+            for i in range(startIndex,n - (k - len(path)) + 2):  #优化的地方
                 path.append(i)  #处理节点 
                 backtrack(n,k,i+1)  #递归
                 path.pop()  #回溯，撤销处理的节点
diff --git a/problems/二叉树的递归遍历.md b/problems/二叉树的递归遍历.md
index 875e6169..0468b79b 100644
--- a/problems/二叉树的递归遍历.md
+++ b/problems/二叉树的递归遍历.md
@@ -409,5 +409,56 @@ int* postorderTraversal(struct TreeNode* root, int* returnSize){
 }
 ```
 
+Swift:
+前序遍历：（144.二叉树的前序遍历）
+```Swift
+func preorderTraversal(_ root: TreeNode?) -> [Int] {
+    var res = [Int]()
+    preorder(root, res: &res)
+    return res
+}
+func preorder(_ root: TreeNode?, res: inout [Int]) {
+    if root == nil {
+        return
+    }
+    res.append(root!.val)
+    preorder(root!.left, res: &res)
+    preorder(root!.right, res: &res)
+}
+```
+
+中序遍历：（94. 二叉树的中序遍历）
+```Swift
+func inorderTraversal(_ root: TreeNode?) -> [Int] {
+    var res = [Int]()
+    inorder(root, res: &res)
+    return res
+}
+func inorder(_ root: TreeNode?, res: inout [Int]) {
+    if root == nil {
+        return
+    }
+    inorder(root!.left, res: &res)
+    res.append(root!.val)
+    inorder(root!.right, res: &res)
+}
+```
+
+后序遍历：（145. 二叉树的后序遍历）
+```Swift
+func postorderTraversal(_ root: TreeNode?) -> [Int] {
+    var res = [Int]()
+    postorder(root, res: &res)
+    return res
+}
+func postorder(_ root: TreeNode?, res: inout [Int]) {
+    if root == nil {
+        return
+    }
+    postorder(root!.left, res: &res)
+    postorder(root!.right, res: &res)
+    res.append(root!.val)
+}
+```
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>