private static int DFS(TreeNode node) {
		if (node.left == null && node.right == null) {
			return 1;
		}
		if (node.left != null && node.right == null) {
			return DFS(node.left) + 1;
		}
		if (node.left == null && node.right != null) {
			return DFS(node.right) + 1;
		}

		return Math.min(DFS(node.left), DFS(node.right)) + 1;

	}