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.
思路:recursion 解决subproblem,也就是分两种情况,左右分别相等和左右互换;
/**
* 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;
}
if(root1 == null || root2 == null) {
return false;
}
if(root1.val != root2.val) {
return false;
}
return
(flipEquiv(root1.left, root2.left)
&& flipEquiv(root1.right, root2.right))
||
(flipEquiv(root1.right, root2.left)
&& flipEquiv(root1.left, root2.right));
}
}