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题目
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,null,null,7,8], root2 = [1,3,2,null,6,4,5,null,null,null,null,8,7]
Output: true
Explanation: We flipped at nodes with values 1, 3, 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].
题目地址
讲解
这道题考察的依旧是递归，其实跟树有关的大部分题都是递归。树对应多叉递归，栈对应线性递归。然后递归重要的就一个点：结束条件。
Java 代码
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) {val = x;}
* }
*/
class Solution {
public boolean flipEquiv(TreeNode root1, TreeNode root2) {
if(root1==null && root2==null){
return true;
}else if((root1==null&&root2!=null) || (root1!=null&&root2==null) || (root1.val!=root2.val)){
return false;
}
return (flipEquiv(root1.left, root2.left) && flipEquiv(root1.right, root2.right)) || (flipEquiv(root1.left, root2.right) && flipEquiv(root1.right, root2.left));
}
}
