Merge pull request #1004 from qxuewei/master

添加 101. 对称二叉树 Swift版本

problems/0101.对称二叉树.md

@@ -574,7 +574,87 @@ var isSymmetric = function(root) {
 };
 ```
 
+## Swift:
 
+> 递归
+```swift
+func isSymmetric(_ root: TreeNode?) -> Bool {
+    return _isSymmetric(root?.left, right: root?.right)
+}
+func _isSymmetric(_ left: TreeNode?, right: TreeNode?) -> Bool {
+    // 首先排除空节点情况
+    if left == nil && right == nil {
+        return true
+    } else if left == nil && right != nil {
+        return false
+    } else if left != nil && right == nil {
+        return false
+    } else if left!.val != right!.val {
+        // 进而排除数值不相等的情况
+        return false
+    }
+    
+    // left 和 right 都不为空, 且数值也相等就递归
+    let inSide = _isSymmetric(left!.right, right: right!.left)
+    let outSide = _isSymmetric(left!.left, right: right!.right)
+    return inSide && outSide
+}
+```
+
+> 迭代 - 使用队列
+```swift
+func isSymmetric2(_ root: TreeNode?) -> Bool {
+    guard let root = root else {
+        return true
+    }
+    var queue = [TreeNode?]()
+    queue.append(root.left)
+    queue.append(root.right)
+    while !queue.isEmpty {
+        let left = queue.removeFirst()
+        let right = queue.removeFirst()
+        if left == nil && right == nil {
+            continue
+        }
+        if left == nil || right == nil || left?.val != right?.val {
+            return false
+        }
+        queue.append(left!.left)
+        queue.append(right!.right)
+        queue.append(left!.right)
+        queue.append(right!.left)
+    }
+    return true
+}
+```
+
+> 迭代 - 使用栈
+```swift
+func isSymmetric3(_ root: TreeNode?) -> Bool {
+    guard let root = root else {
+        return true
+    }
+    var stack = [TreeNode?]()
+    stack.append(root.left)
+    stack.append(root.right)
+    while !stack.isEmpty {
+        let left = stack.removeLast()
+        let right = stack.removeLast()
+        
+        if left == nil && right == nil {
+            continue
+        }
+        if left == nil || right == nil || left?.val != right?.val {
+            return false
+        }
+        stack.append(left!.left)
+        stack.append(right!.right)
+        stack.append(left!.right)
+        stack.append(right!.left)
+    }
+    return true
+}
+```
 
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0104.二叉树的最大深度.md

@@ -653,5 +653,82 @@ int maxDepth(struct TreeNode* root){
 }
 ```
 
+## Swift
+
+>二叉树最大深度
+```swift
+// 递归 - 后序
+func maxDepth1(_ root: TreeNode?) -> Int {
+    return _maxDepth1(root)
+}
+func _maxDepth1(_ root: TreeNode?) -> Int {
+    if root == nil {
+        return 0
+    }
+    let leftDepth = _maxDepth1(root!.left)
+    let rightDepth = _maxDepth1(root!.right)
+    return 1 + max(leftDepth, rightDepth)
+}
+
+// 层序
+func maxDepth(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    var queue = [TreeNode]()
+    queue.append(root)
+    var res: Int = 0
+    while !queue.isEmpty {
+        res += 1
+        for _ in 0 ..< queue.count {
+            let node = queue.removeFirst()
+            if let left = node.left {
+                queue.append(left)
+            }
+            if let right = node.right {
+                queue.append(right)
+            }
+        }
+    }
+    return res
+}
+```
+
+>N叉树最大深度
+```swift
+// 递归
+func maxDepth(_ root: Node?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    var depth = 0
+    for node in root.children {
+        depth = max(depth, maxDepth(node))
+    }
+    return depth + 1
+}
+
+// 迭代-层序遍历
+func maxDepth1(_ root: Node?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    var depth = 0
+    var queue = [Node]()
+    queue.append(root)
+    while !queue.isEmpty {
+        let size = queue.count
+        depth += 1
+        for _ in 0 ..< size {
+            let node = queue.removeFirst()
+            for child in node.children {
+                queue.append(child)
+            }
+        }
+    }
+    return depth
+}
+```
+
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0111.二叉树的最小深度.md

@@ -404,8 +404,51 @@ var minDepth = function(root) {
 };
 ```
 
+## Swift
 
+> 递归
+```Swift
+func minDepth(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    if root.left == nil && root.right != nil {
+        return 1 + minDepth(root.right)
+    }
+    if root.left != nil && root.right == nil {
+        return 1 + minDepth(root.left)
+    }
+    return 1 + min(minDepth(root.left), minDepth(root.right))
+}
+```
 
+> 迭代
+```Swift
+func minDepth(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    var res = 0
+    var queue = [TreeNode]()
+    queue.append(root)
+    while !queue.isEmpty {
+        res += 1
+        for _ in 0 ..< queue.count {
+            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)
+            }
+        }
+    }
+    return res
+}
+```
 
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0222.完全二叉树的节点个数.md

@@ -522,5 +522,73 @@ int countNodes(struct TreeNode* root){
 }
 ```
 
+## Swift:
+
+> 递归
+```swift
+func countNodes(_ root: TreeNode?) -> Int {
+    return _countNodes(root)
+}
+func _countNodes(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    let leftCount = _countNodes(root.left)
+    let rightCount = _countNodes(root.right)
+    return 1 + leftCount + rightCount
+}
+```
+  
+> 层序遍历
+```Swift
+func countNodes(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    var res = 0
+    var queue = [TreeNode]()
+    queue.append(root)
+    while !queue.isEmpty {
+        let size = queue.count
+        for _ in 0 ..< size {
+            let node = queue.removeFirst()
+            res += 1
+            if let left = node.left {
+                queue.append(left)
+            }
+            if let right = node.right {
+                queue.append(right)
+            }
+        }
+    }
+    return res
+}
+```
+  
+> 利用完全二叉树性质
+```Swift
+func countNodes(_ root: TreeNode?) -> Int {
+    guard let root = root else {
+        return 0
+    }
+    var leftNode = root.left
+    var rightNode = root.right
+    var leftDepth = 0
+    var rightDepth = 0
+    while leftNode != nil {
+        leftNode = leftNode!.left
+        leftDepth += 1
+    }
+    while rightNode != nil {
+        rightNode = rightNode!.right
+        rightDepth += 1
+    }
+    if leftDepth == rightDepth {
+        return (2 << leftDepth) - 1
+    }
+    return countNodes(root.left) + countNodes(root.right) + 1
+}
+```
+
 -----------------------
 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>