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(isMirror(root,root))
     return true;
     else
     return false;
    }
    public boolean isMirror(TreeNode l, TreeNode r){
        if(l==null&&r==null)
        return true;
        if((l!=null)&&(r!=null)&&(l.val==r.val))
        if(isMirror(l.left,r.right)&&isMirror(l.right,r.left))
        return true;
        return false;
        
    }
}
Iterative way, kind of complex
public class Solution {
    public boolean isSymmetric(TreeNode root) {
    return isMirror(root,root);
    }
    public boolean isMirror(TreeNode l, TreeNode r){
        if(l==null&&r==null)
        return true;
        Queue<ArrayList<TreeNode>> tmp=new LinkedList<ArrayList<TreeNode>>();
        ArrayList<TreeNode> res= new ArrayList<TreeNode> ();
        res.add(l);
        res.add(r);
        tmp.offer(res);
        while(!tmp.isEmpty()){
            ArrayList<TreeNode>head=tmp.poll();
  
                TreeNode l1=head.get(0);
	            TreeNode r1=head.get(1);
	            if(l1==null&&r1==null)
	            continue;
            if(l1!=null&&r1!=null&&l1.val==r1.val){
                ArrayList<TreeNode> temp1=new ArrayList<TreeNode>();
                ArrayList<TreeNode> temp2=new ArrayList<TreeNode>();
             temp1.add(l1.left);
                temp1.add(r1.right);
                tmp.offer(temp1);
                temp2.add(l1.right);
                temp2.add(r1.left);
                tmp.offer(temp2);
            }
            else
            return false;
            
            
        }
        return true;
    }
}
/**
 * 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) {
        
        Queue<TreeNode> queue=new LinkedList<TreeNode>();
        queue.offer(root);
        queue.offer(root);//精髓在你先导入两个root进去，因为没有mirror，你需要创造mirror， 而且l和r需要两个一样的node
        while(!queue.isEmpty()){
            TreeNode l=queue.poll();
            TreeNode r=queue.poll();
            if(l==null&&r==null)
            continue;
            if(l!=null&&r!=null&&l.val==r.val){
                queue.offer(l.left);
                queue.offer(r.right);
                queue.offer(l.right);
                queue.offer(r.left);
            }
            else     //千万别忘了
            return false;
            
        }
        return true;
        
    }
}