diff --git a/problems/0102.二叉树的层序遍历.md b/problems/0102.二叉树的层序遍历.md
index 74485848..4951631c 100644
--- a/problems/0102.二叉树的层序遍历.md
+++ b/problems/0102.二叉树的层序遍历.md
@@ -273,32 +273,29 @@ function levelOrder(root: TreeNode | null): number[][] {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func levelOrder(_ root: TreeNode?) -> [[Int]] {
-    var res = [[Int]]()
-    guard let root = root else {
-        return res
-    }
-    var queue = [TreeNode]()
-    queue.append(root)
+    var result = [[Int]]()
+    guard let root = root else { return result }
+    // 表示一层
+    var queue = [root]
     while !queue.isEmpty {
-        let size = queue.count
-        var sub = [Int]()
-        for _ in 0 ..< size {
+        let count = queue.count
+        var subarray = [Int]()
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            sub.append(node.val)
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
-            }
+            subarray.append(node.val)
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
         }
-        res.append(sub)
+        result.append(subarray)
     }
-    return res
+
+    return result
 }
 ```
 
@@ -505,30 +502,29 @@ function levelOrderBottom(root: TreeNode | null): number[][] {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func levelOrderBottom(_ root: TreeNode?) -> [[Int]] {
-    var res =  [[Int]]()
-    guard let root = root else {
-        return res
-    }
-    var queue:  [TreeNode] = [root]
+    // 表示一层
+    var queue = [TreeNode]()
+    if let node = root { queue.append(node) }
+    var result = [[Int]]()
     while !queue.isEmpty {
-        var sub = [Int]()
-        for _ in 0 ..< queue.count {
+        let count = queue.count
+        var subarray = [Int]()
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            sub.append(node.val)
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
-            }
+            subarray.append(node.val)
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node)}
         }
-        res.insert(sub, at: 0)
+        result.append(subarray)
     }
-    return res
+
+    return result.reversed()
 }
 ```
 
@@ -729,37 +725,31 @@ function rightSideView(root: TreeNode | null): number[] {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func rightSideView(_ root: TreeNode?) -> [Int] {
-    var res = [Int]()
-    guard let root = root else {
-        return res
-    }
+    // 表示一层
     var queue = [TreeNode]()
-    queue.append(root)
+    if let node = root { queue.append(node) }
+    var result = [Int]()
     while !queue.isEmpty {
-        let size = queue.count
-        for i in 0 ..< size {
+        let count = queue.count
+        for i in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            if i == size - 1 {
-                // 保存 每层最后一个元素
-                res.append(node.val)
-            }
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
-            }
+            if i == count - 1 { result.append(node.val) }
+
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
         }
     }
-    return res
+
+    return result
 }
 ```
 
-
 # 637.二叉树的层平均值
 
 [力扣题目链接](https://leetcode-cn.com/problems/average-of-levels-in-binary-tree/)
@@ -965,32 +955,30 @@ function averageOfLevels(root: TreeNode | null): number[] {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func averageOfLevels(_ root: TreeNode?) -> [Double] {
-    var res = [Double]()
-    guard let root = root else {
-        return res
-    }
+    // 表示一层
     var queue = [TreeNode]()
-    queue.append(root)
+    if let node = root { queue.append(node) }
+    var result = [Double]()
     while !queue.isEmpty {
-        let size = queue.count
+        let count = queue.count
         var sum = 0
-        for _ in 0 ..< size {
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
             sum += node.val
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
-            }
+
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
         }
-        res.append(Double(sum) / Double(size))
+        result.append(Double(sum) / Double(count))
     }
-    return res
+
+    return result
 }
 ```
 
@@ -1212,29 +1200,28 @@ function levelOrder(root: Node | null): number[][] {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func levelOrder(_ root: Node?) -> [[Int]] {
-    var res = [[Int]]()
-    guard let root = root else {
-        return res
-    }
+    // 表示一层
     var queue = [Node]()
-    queue.append(root)
+    if let node = root { queue.append(node) }
+    var result = [[Int]]()
     while !queue.isEmpty {
-        let size = queue.count
-        var sub = [Int]()
-        for _ in 0 ..< size {
+        let count = queue.count
+        var subarray = [Int]()
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            sub.append(node.val)
-            for childNode in node.children {
-                queue.append(childNode)
-            }
+            subarray.append(node.val)
+            // 下一层
+            for node in node.children { queue.append(node) }
         }
-        res.append(sub)
+        result.append(subarray)
     }
-    return res
+
+    return result
 }
 ```
 
@@ -1419,34 +1406,30 @@ function largestValues(root: TreeNode | null): number[] {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func largestValues(_ root: TreeNode?) -> [Int] {
-    var res = [Int]()
-    guard let root = root else {
-        return res
-    }
+    // 表示一层
     var queue = [TreeNode]()
-    queue.append(root)
+    if let node = root { queue.append(node) }
+    var result = [Int]()
     while !queue.isEmpty {
-        let size = queue.count
-        var max: Int = Int.min
-        for _ in 0 ..< size {
+        let count = queue.count
+        var max = queue[0].val
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            if node.val > max {
-                max = node.val
-            }
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
-            }
+            if node.val > max { max = node.val }
+
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
         }
-        res.append(max)
+        result.append(max)
     }
-    return res
+
+    return result
 }
 ```
 
@@ -1456,7 +1439,7 @@ func largestValues(_ root: TreeNode?) -> [Int] {
 
 给定一个完美二叉树，其所有叶子节点都在同一层，每个父节点都有两个子节点。二叉树定义如下：
 
-```
+```cpp
 struct Node {
   int val;
   Node *left;
@@ -1677,33 +1660,34 @@ func connect(root *Node) *Node {
 }
 ```
 
-Swift:
+Swift：
+
 ```swift
 func connect(_ root: Node?) -> Node? {
-    guard let root = root else {
-        return nil
-    }
+    // 表示一层
     var queue = [Node]()
-    queue.append(root)
+    if let node = root { queue.append(node) }
     while !queue.isEmpty {
-        let size = queue.count
-        var preNode: Node?
-        for i in 0 ..< size {
-            let node = queue.removeFirst()
+        let count = queue.count
+        var current, previous: Node!
+        for i in 0 ..< count {
+            // 当前层
             if i == 0 {
-                preNode = node
+                previous = queue.removeFirst()
+                current = previous
             } else {
-                preNode?.next = node
-                preNode = node
-            }
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
+                current = queue.removeFirst()
+                previous.next = current
+                previous = current
             }
+
+            // 下一层
+            if let node = current.left { queue.append(node) }
+            if let node = current.right { queue.append(node) }
         }
+        previous.next = nil
     }
+
     return root
 }
 ```
@@ -1927,34 +1911,34 @@ func connect(root *Node) *Node {
     return root
 }
 ```
-
 Swift：
+
 ```swift
 func connect(_ root: Node?) -> Node? {
-    guard let root = root else {
-        return nil
-    }
+    // 表示一层
     var queue = [Node]()
-    queue.append(root)
+    if let node = root { queue.append(node) }
     while !queue.isEmpty {
-        let size = queue.count
-        var preNode: Node?
-        for i in 0 ..< size {
-            let node = queue.removeFirst()
+        let count = queue.count
+        var current, previous: Node!
+        for i in 0 ..< count {
+            // 当前层
             if i == 0 {
-                preNode = node
+                previous = queue.removeFirst()
+                current = previous
             } else {
-                preNode?.next = node
-                preNode = node
-            }
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
+                current = queue.removeFirst()
+                previous.next = current
+                previous = current
             }
+
+            // 下一层
+            if let node = current.left { queue.append(node) }
+            if let node = current.right { queue.append(node) }
         }
+        previous.next = nil
     }
+
     return root
 }
 ```
@@ -2151,29 +2135,28 @@ function maxDepth(root: TreeNode | null): number {
 };
 ```
 
-Swift:
+Swift：
 
 ```swift
 func maxDepth(_ root: TreeNode?) -> Int {
-    guard let root = root else {
-        return 0
-    }
+    guard root != nil else { return 0 }
+    var depth = 0
     var queue = [TreeNode]()
-    queue.append(root)
-    var res: Int = 0
+    queue.append(root!)
     while !queue.isEmpty {
-        for _ in 0 ..< queue.count {
+        let count = queue.count
+        depth += 1
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
-            }
+
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
         }
-        res += 1
     }
-    return res
+
+    return depth
 }
 ```
 
@@ -2374,28 +2357,25 @@ Swift：
 
 ```swift
 func minDepth(_ root: TreeNode?) -> Int {
-    guard let root = root else {
-        return 0
-    }
-    var res = 0
-    var queue = [TreeNode]()
-    queue.append(root)
+    guard root != nil else { return 0 }
+    var depth = 0
+    var queue = [root!]
     while !queue.isEmpty {
-        res += 1
-        for _ in 0 ..< queue.count {
+        let count = queue.count
+        depth += 1
+        for _ in 0 ..< count {
+            // 当前层
             let node = queue.removeFirst()
-            if node.left == nil && node.right == nil {
-                return res
-            }
-            if let left = node.left {
-                queue.append(left)
-            }
-            if let right = node.right {
-                queue.append(right)
+            if node.left == nil, node.right == nil { // 遇到叶子结点则返回
+                return depth
             }
+
+            // 下一层
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
         }
     }
-    return res
+    return depth
 }
 ```
 
diff --git a/problems/0226.翻转二叉树.md b/problems/0226.翻转二叉树.md
index 8108e7ad..a3ebe24d 100644
--- a/problems/0226.翻转二叉树.md
+++ b/problems/0226.翻转二叉树.md
@@ -47,8 +47,6 @@
 
 ## 递归法
 
-
-
 对于二叉树的递归法的前中后序遍历，已经在[二叉树：前中后序递归遍历](https://programmercarl.com/二叉树的递归遍历.html)详细讲解了。
 
 我们下文以前序遍历为例，通过动画来看一下翻转的过程:
@@ -63,7 +61,7 @@
 
 返回值的话其实也不需要，但是题目中给出的要返回root节点的指针，可以直接使用题目定义好的函数，所以就函数的返回类型为`TreeNode*`。
 
-```
+```cpp
 TreeNode* invertTree(TreeNode* root)
 ```
 
@@ -71,7 +69,7 @@ TreeNode* invertTree(TreeNode* root)
 
 当前节点为空的时候，就返回
 
-```
+```cpp
 if (root == NULL) return root;
 ```
 
@@ -79,7 +77,7 @@ if (root == NULL) return root;
 
 因为是先前序遍历，所以先进行交换左右孩子节点，然后反转左子树，反转右子树。
 
-```
+```cpp
 swap(root->left, root->right);
 invertTree(root->left);
 invertTree(root->right);
@@ -257,7 +255,7 @@ public:
 ## 其他语言版本
 
 
-### Java：
+### Java
 
 ```Java
 //DFS递归
@@ -469,8 +467,6 @@ func invertTree(root *TreeNode) *TreeNode {
 }
 ```
 
-
-
 ### JavaScript
 
 使用递归版本的前序遍历
@@ -690,7 +686,7 @@ function invertTree(root: TreeNode | null): TreeNode | null {
 };
 ```
 
-### C:
+### C
 
 递归法
 ```c
@@ -775,5 +771,54 @@ func invertTree1(_ root: TreeNode?) -> TreeNode? {
 }
 ```
 
+### Swift
+
+深度优先递归。
+
+```swift
+func invertTree(_ root: TreeNode?) -> TreeNode? {
+    guard let node = root else { return root }
+    swap(&node.left, &node.right)
+    _ = invertTree(node.left)
+    _ = invertTree(node.right)
+    return root
+}
+```
+
+深度优先迭代，子结点顺序不重要，从根结点出发深度遍历即可。
+
+```swift
+func invertTree(_ root: TreeNode?) -> TreeNode? {
+    guard let node = root else { return root }
+    var stack = [node]
+    while !stack.isEmpty {
+        guard let node = stack.popLast() else { break }
+        swap(&node.left, &node.right)
+        if let node = node.left { stack.append(node) }
+        if let node = node.right { stack.append(node) }
+    }
+    return root
+}
+```
+
+广度优先迭代。
+
+```swift
+func invertTree(_ root: TreeNode?) -> TreeNode? {
+    guard let node = root else { return root }
+    var queue = [node]
+    while !queue.isEmpty {
+        let count = queue.count
+        for _ in 0 ..< count {
+            let node = queue.removeFirst()
+            swap(&node.left, &node.right)
+            if let node = node.left { queue.append(node) }
+            if let node = node.right { queue.append(node) }
+        }
+    }
+    return root
+}
+```
+
 -----------------------
 <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/二叉树的迭代遍历.md b/problems/二叉树的迭代遍历.md
index ba38726b..8164724b 100644
--- a/problems/二叉树的迭代遍历.md
+++ b/problems/二叉树的迭代遍历.md
@@ -390,7 +390,7 @@ func inorderTraversal(root *TreeNode) []int {
 }
 ```
 
-javaScript
+javaScript：
 
 ```js
 
@@ -454,7 +454,7 @@ var postorderTraversal = function(root, res = []) {
 };
 ```
 
-TypeScript:
+TypeScript：
 
 ```typescript
 // 前序遍历（迭代法）
@@ -509,77 +509,63 @@ function postorderTraversal(root: TreeNode | null): number[] {
 };
 ```
 
-Swift:
+Swift：
 
-> 迭代法前序遍历
 ```swift
+// 前序遍历迭代法
 func preorderTraversal(_ root: TreeNode?) -> [Int] {
-    var res = [Int]()
-    if root == nil {
-        return res
-    }
-    var stack = [TreeNode]()
-    stack.append(root!)
+    var result = [Int]()
+    guard let root = root else { return result }
+    var stack = [root]
     while !stack.isEmpty {
-        let node = stack.popLast()!
-        res.append(node.val)
-        if node.right != nil {
-            stack.append(node.right!)
+        let current = stack.removeLast()
+        // 先右后左，这样出栈的时候才是左右顺序
+        if let node = current.right { // 右
+            stack.append(node)
         }
-        if node.left != nil {
-            stack.append(node.left!)
+        if let node = current.left { // 左
+            stack.append(node)
         }
+        result.append(current.val) // 中
     }
-    return res
+    return result
 }
-```
 
-> 迭代法中序遍历
-```swift
-func inorderTraversal(_ root: TreeNode?) -> [Int] {
-    var res = [Int]()
-    if root == nil {
-        return res
-    }
-    var stack = [TreeNode]()
-    var cur: TreeNode? = root
-    while cur != nil || !stack.isEmpty {
-        if cur != nil {
-            stack.append(cur!)
-            cur = cur!.left
-        } else {
-            cur = stack.popLast()
-            res.append(cur!.val)
-            cur = cur!.right
-        }
-    }
-    return res
-}
-```
-
-> 迭代法后序遍历
-```swift
+// 后序遍历迭代法
 func postorderTraversal(_ root: TreeNode?) -> [Int] {
-    var res = [Int]()
-    if root == nil {
-        return res
-    }
-    var stack = [TreeNode]()
-    stack.append(root!)
-    // res 存储 中 -> 右 -> 左
+    var result = [Int]()
+    guard let root = root else { return result }
+    var stack = [root]
     while !stack.isEmpty {
-        let node = stack.popLast()!
-        res.append(node.val)
-        if node.left != nil  {
-            stack.append(node.left!)
+        let current = stack.removeLast()
+        // 与前序相反，即中右左，最后结果还需反转才是后序
+        if let node = current.left { // 左
+            stack.append(node)
         }
-        if node.right != nil  {
-            stack.append(node.right!)
+        if let node = current.right { // 右
+            stack.append(node)
+        }
+        result.append(current.val) // 中
+    }
+    return result.reversed()
+}
+
+// 中序遍历迭代法
+func inorderTraversal(_ root: TreeNode?) -> [Int] {
+    var result = [Int]()
+    var stack = [TreeNode]()
+    var current: TreeNode! = root
+    while current != nil || !stack.isEmpty {
+        if current != nil { // 先访问到最左叶子
+            stack.append(current)
+            current = current.left // 左
+        } else {
+            current = stack.removeLast()
+            result.append(current.val) // 中
+            current = current.right // 右
         }
     }
-    // res 翻转
-    res.reverse()
-    return res
+    return result
 }
 ```
 
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 2fef68da..35d19d7b 100644
--- a/problems/二叉树的递归遍历.md
+++ b/problems/二叉树的递归遍历.md
@@ -34,19 +34,19 @@
 
 1. **确定递归函数的参数和返回值**：因为要打印出前序遍历节点的数值，所以参数里需要传入vector在放节点的数值，除了这一点就不需要在处理什么数据了也不需要有返回值，所以递归函数返回类型就是void，代码如下：
 
-```
+```cpp
 void traversal(TreeNode* cur, vector<int>& vec)
 ```
 
 2. **确定终止条件**：在递归的过程中，如何算是递归结束了呢，当然是当前遍历的节点是空了，那么本层递归就要要结束了，所以如果当前遍历的这个节点是空，就直接return，代码如下：
 
-```
+```cpp
 if (cur == NULL) return;
 ```
 
 3. **确定单层递归的逻辑**：前序遍历是中左右的循序，所以在单层递归的逻辑，是要先取中节点的数值，代码如下：
 
-```
+```cpp
 vec.push_back(cur->val);    // 中
 traversal(cur->left, vec);  // 左
 traversal(cur->right, vec); // 右