week 3 101. Symmetric Tree

/**
 * 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;
        }
       Queue<TreeNode> que = new LinkedList<>();
       que.add(root.left);
       que.add(root.right);
       while(!que.isEmpty()){
           TreeNode left = que.remove();
           TreeNode right = que.remove ();
           if(left == null && right == null){
               continue;
           }
           if(left == null || right == null){
               return false;
           }
        if(left.val != right.val){
            return false;
        }
        que.add(left.left);
        que.add(right.right);
        que.add(left.right);
        que.add(right.left);
       }
       return true;
    }
}