(java)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.

思路:本题就是判断一个二叉树是不是对称的，树的每一层都可以用水仙花数的判断方法进行判断，只要有一层不是水仙花数就不是对称的树。

代码如下(已通过leetcode)

public class Solution {

public boolean isSymmetric(TreeNode root) {

if(root==null) return true;

return isequal(root.left,root.right);

}

//

public boolean isequal(TreeNode p,TreeNode q) {

if(p==null || q==null) return p==q;

return p.val==q.val && isequal(p.left,q.right) && isequal(p.right,q.left);

}

}