Dart implementation of counting the number of components in the graph and finding the size of the largest component in it.

graph-component-size-count.dart

/// find the number of connected components within the undirected graph.
/// Component is independent or individual graph within the graph-network
/// Also getting the size of the largest component in it.
const graph = {
  0: [8, 1, 5],
  1: [0],
  5: [0, 8],
  8: [0, 5],
  2: [3, 4],
  3: [2, 4],
  4: [3, 2]
};

void main() {
  print("Number of components <-> Largest component size : " + getComponents().toString());
}

final visited = <int>{};
String getComponents() {
  int largest = 0;
  int last = 0;
  int components = 0;
  for (final key in graph.keys) {
    components += helper(key);
    if(largest < visited.length - last){
      largest = visited.length - last;
    }
    last = visited.length;
  }
  return (components.toString() + " <-> " + largest.toString());
}

int helper(int key) {
  if (visited.contains(key)) {
    return 0;
  }
  visited.add(key);

  for (final neighbor in graph[key]!) {
    helper(neighbor);
  }
  return 1;
}