添加 222.完全二叉树的节点个数 Swift版本

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
+}
+```
+
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>