101 Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

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


 public boolean isSymmetric(TreeNode root) {
       return mirror(root,root);
    }
    
    
    boolean mirror(TreeNode a, TreeNode b){
        if(a==null && b==null)      return true;
        else if(a==null || b==null) return false;
        else if(a.val != b.val) return false;
        
        else{
           return mirror(a.left,b.right) && mirror(a.right,b.left);
            //true && true = true
            //false && true = false
            //false && false = false
        }
    }
    
  

//Approach

    1                         //COPY 
   / \
  2   2   (left = right)      
 / \ / \
3  4 4  3 (left = right)
        
        //Case1 a== null && b==null    true
        //Case2 a==null || b==null     false
        //Case3 a.val != b.val         false
        
        //-------------MOVE-------------