[Swift]LeetCode226. 翻转二叉树 | Invert Binary Tree

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Invert a binary tree.

Example:

Input:

     4
   /   
  2     7
 /    / 
1   3 6   9

Output:

     4
   /   
  7     2
 /    / 
9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.

---

翻转一棵二叉树。

示例：

输入：

     4
   /   
  2     7
 /    / 
1   3 6   9

输出：

     4
   /   
  7     2
 /    / 
9   6 3   1

备注:
这个问题是受到 Max Howell 的 原问题 启发的 ：

谷歌：我们90％的工程师使用您编写的软件(Homebrew)，但是您却无法在面试时在白板上写出翻转二叉树这道题，这太糟糕了。

---

12ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func invertTree(_ root: TreeNode?) -> TreeNode? {
        guard let root = root else {return nil}
        let left = invertTree(root.left)
        let right = invertTree(root.right)
        root.left = right
        root.right = left
        return root
    }
}

---

8ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func invertTree(_ root: TreeNode?) -> TreeNode? {
        if root == nil {
            return root
        }else{
            let temp = root?.left
            root?.left = invertTree(root?.right)
            root?.right = invertTree(temp)
            return root
        }
    }
}

---

---

12ms

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func invertTree(_ root: TreeNode?) -> TreeNode? {
        if root == nil {
        return root
    }
    
    var temp: TreeNode?
    
    if root?.left?.left != nil || root?.left?.right != nil {
        temp = invertTree(root?.left)
    }else {
        temp = root?.left
    }
    if (root?.right?.left != nil || root?.right?.right != nil ){
        root?.left = invertTree(root?.right)
    }else {
        root?.left = root?.right
    }
    root?.right = temp
    
    return root
        
    }
}