Random binary tree

main.dart

import 'dart:math';

const maxNodes = 10;

void main() {
  final rng = Random();
  final nodes = List.generate(maxNodes, (index) => Node(index + 1));
  final openNodes = [nodes[0]];
  nodes.skip(1).forEach((node) {
    node.parent = openNodes[rng.nextInt(openNodes.length)];
    openNodes.add(node);
    if (node.parent.right != null ||
        (node.parent.left == null && rng.nextBool()))
      node.parent.left = node;
    else
      node.parent.right = node;
    if (!node.parent.isOpen) openNodes.remove(node.parent);
  });
  nodes.forEach(print);
}

class Node {
  Node(this.id);
  final int id;
  Node parent;
  Node left;
  Node right;
  bool get isOpen => left == null || right == null;
  @override
  String toString() => '$id: (${left?.id ?? '_'}, ${right?.id ?? '_'})';
}