LeetCode_101. Symmetric Tree_对称二叉树

101. 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.

如题，判断一个二叉树是否是对称的。

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

if (left == null || right == null)
return false;

if (left.val != right.val)
return false;

return MirrorTree(left.left, right.right) && MirrorTree(left.right, right.left);
}
}