【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
    
     5

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

 

/**
 * Definition for binary tree
 * 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 isMir(root.left,root.right);
        }
        return true;
    }

    private boolean isMir(TreeNode left, TreeNode right) {
        // TODO Auto-generated method stub
        if(left==null&&right!=null)
            return false;
        if(left!=null&&right==null)
            return false;
        if(left==null&&right==null)
            return true;
        if(left.val!=right.val)
            return false;
        
        return isMir(left.left,right.right)&&isMir(left.right,right.left);
    }
}