//最深
    public int maxDepth(TreeNode root) {
        return traveel(root, 0, 0);
    }

    public int traveel(TreeNode node, int max, int dep){
        if (node == null) return max;
        dep++;
        if (node.left == null && node.right == null){
            //到达最低节点，判断最大值
            return Math.max(dep, max);
        }else{
            return Math.max(traveel(node.left, max, dep), traveel(node.right, max, dep));
        }
    }

    //最浅
   public int minDepth(TreeNode root) {
        if (root == null) return 0;
        return traveel(root, Integer.MAX_VALUE, 0);
    }

    public int traveel(TreeNode node, int min, int dep){
        if (node == null) return min;
        dep++;
        if (node.left == null && node.right == null){
            //到达最低节点，判断最大值
            return Math.min(dep, min);
        }else{
            return Math.min(traveel(node.left, min, dep), traveel(node.right, min, dep));
        }
    }