[Swift Weekly Contest 113]LeetCode951. 翻转等价二叉树 | Flip Equivalent Binary Trees

概述For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees. A binary tree X is flip equivalent to a binary tree Y if and only if we can

For a binary tree T,we can define a flip operation as follows: choose any node,and swap the left and right child subtrees.

A binary tree X is flip equivalent to a binary tree Y if and only if we can make X equal to Y after some number of flip operations.

Write a function that determines whether two binary trees are flip equivalent.  The trees are given by root nodes root1 and root2. 

Example 1:

input: root1 = [1,2,3,4,5,6,null,7,8],root2 = [1,8,7] Output: true Explanation: We flipped at nodes with values 1,and 5. 

 

Note:

Each tree will have at most 100 nodes. Each value in each tree will be a unique integer in the range [0,99].

我们可以为二叉树 T 定义一个翻转 *** 作，如下所示：选择任意节点，然后交换它的左子树和右子树。

只要经过一定次数的翻转 *** 作后，能使 X 等于 Y，我们就称二叉树 X 翻转等价于二叉树 Y。

编写一个判断两个二叉树是否是翻转等价的函数。这些树由根节点 root1和 root2 给出。

示例：

输入：root1 = [1,root2 = [1,7]输出：true解释：We flipped at nodes with values 1,and 5.

 

提示：

每棵树最多有 100 个节点。 每棵树中的每个值都是唯一的、在 [0,99] 范围内的整数。

16ms

 1 /** 2  * DeFinition for a binary tree node. 3  * public class TreeNode { 4  *     public var val: Int 5  *     public var left: TreeNode? 6  *     public var right: TreeNode? 7  *     public init(_ val: Int) { 8  *         self.val = val 9  *         self.left = nil10  *         self.right = nil11  *     }12  * }13  */14 class Solution {15     func flipEquiv(_ root1: TreeNode?,_ root2: TreeNode?) -> Bool {16         if root1 == nil {return root2 == nil}17         if root2 == nil {return root1 == nil}18         if root1!.val != root2!.val {return false}19         if flipEquiv(root1!.left,root2!.left) && flipEquiv(root1!.right,root2!.right)20         {21             return true22         }23         if flipEquiv(root1!.left,root2!.right) && flipEquiv(root1!.right,root2!.left)24         {25             return true26         }27         return false28     }29 }

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