LeetCode Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

1 / \ 2 2 / \ / \3 4 4 3

But the following is not:

1 / \ 2 2 \ \ 3 3

Note:Bonus points if you could solve it both recursively and iteratively.

confused what"{1,#,2,3}"means?> read more on how binary tree is serialized on OJ.

OJ’s Binary Tree Serialization:

The serialization of a binary tree follows a level order traversal, where ‘#’ signifies a path terminator where no node exists below.

Here’s an example:

1 / \ 2 3/ 4\5The above binary tree is serialized as"{1,2,3,#,#,4,#,#,5}".

题意：求二叉树是不是对称的。

思路：递归，判断对称的两个节点是否相同。

/** * Definition for binary tree * public class TreeNode { *int val; *TreeNode left; *TreeNode right; *TreeNode(int x) { val = x; } * } */public class Solution {private boolean isSameNode(TreeNode left, TreeNode right) {if (left == null && right == null) return true;if (left == null || right == null) return false;return (left.val == right.val) && isSameNode(left.left, right.right) &&isSameNode(left.right, right.left);}public boolean isSymmetric(TreeNode root) {if (root == null) return true;return isSameNode(root.left, root.right);}}

，也站在未路让我牵挂的人。