Method isSymmetric

Java/symmetric-tree.java:13–18

(TreeNode root)

 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
	/* if root node of tree itself is null, then it's symmetric */
        if(root==null)
            return true;
        return checkMirror(root.left, root.right);
    }
    public boolean checkMirror(TreeNode lt, TreeNode rt){
	/* if root's left and root's right both are null, is then that subtree is symmetric */
        if(lt==null && rt==null)