Maximum Depth of Binary Tree

    public int maxDepth(TreeNode root) {
        //http://blog.csdn.net/linhuanmars/article/details/19659525
        if(root==null) return 0;
        int lev = 0, curNum=1, nextNum=0;
        LinkedList<TreeNode> q = new LinkedList<TreeNode>();
        q.add(root);
        while(!q.isEmpty()){
            curNum--;
            TreeNode n = q.poll();
            if(n.left!=null){
                q.add(n.left);
                nextNum++;
            }
            if(n.right!=null){
                q.add(n.right);
                nextNum++;
            }
            if(curNum==0){
                lev++;
                curNum = nextNum;
                nextNum=0;
            }
        }
        return lev;
    }