[LeetCode]Symmetric Tree

1
   / \
  2   2
 / \ / \
3  4 4  3

1
   / \
  2   2
   \   \
   3    3

/**
 * 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) {
        return helper(root,root);
    }
    private boolean helper(TreeNode root1,TreeNode root2){
        //base case
        if(root1==root2&&root1==null)
            return true;
        if(root1==null||root2==null)
            return false;
        return root1.val==root2.val&&
                helper(root1.left,root2.right)&&
                helper(root1.right,root2.left);
    }
}