'}';
        }
    }

    private static class GraphEdge {
        private final Node from;
        private final Node to;

        private GraphEdge(Node from, Node to) {
            this.from = from;
            this.to = to;
        }

        @Override
        public String toString() {
            return "GraphEdge{" +
                "from=" + from +
                ", to=" + to +