leetcode讲解--951. Flip Equivalent Binary Trees

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: trueExplanation: 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)); }}