题目描述：
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
解题思路：
递归法
代码如下：
/**
* 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;
return isMirror(root.left, root.right);
}
public boolean isMirror(TreeNode left, TreeNode right){
if(left == null && right == null)
return true;
else if(left == null)
return false;
else if(right == null)
return false;
else{
if(left.val != right.val)
return false;
return isMirror(left.right, right.left) && isMirror(left.left, right.right);
}
}
}
Java [Leetcode 101]Symmetric Tree
原文：http://www.cnblogs.com/zihaowang/p/5128196.html