4.1 Implement a function to check if a tree is balanced. For the purposes of this question, a balanced tree is defined to be a tree such that no two leaf nodes differ in distance from the root by more than one.

A balanced tree?

http://en.wikipedia.org/wiki/Self-balancing_binary_search_tree

Iterate the tree, track root-distance for all leaf nodes?

boolean isBalanceTree(Node root)
{
  List<Integer> leafDis = initList();
  visit(root, 0, leafDis);

  return max(leafDis) - min(leafDis) > 1;
}

private void visit(Node n, int curDis, List<Integer> leafDis)
{
  if (n.childrean == null)
    leafDis.add(curDis);
    
  for (Node child : n.children)
  {
    visit(child, curDis + 1, leafDis);
  }
}

CC150 4.1