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

But the following [1,2,2,null,3,null,3] is not:

    1
   / \
  2   2
   \   \
    3    3

Note:
Bonus points if you could solve it both recursively and iteratively.

/**
 * 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 same(root.left,root.right);
 
    }
    public boolean same(TreeNode l,TreeNode r){
       if(l==null&&r==null){
           return true;
       }else if(l==null&&r!=null){
           return false;
       }else if(l!=null&&r==null){
           return  false;
       }else {
           if(l.val==r.val){
               return same(l.left,r.right)&&same(l.right,r.left);
                        
           }else {
               return false;
           }
       }
    }
}

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isSymmetric = function(root) {
    if(!root) return true;
    var stack = [root.left, root.right];
    while(stack.length) {
        var p = stack.pop();
        var q = stack.pop();
        if (p === q) continue;
        if (p && q && p.val === q.val) {
            stack.push(p.left, q.right, p.right, q.left);
        } else {
            return false;
        }
    }
    return true;
};