Java [Leetcode 101]Symmetric Tree

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);
}
}
}