Finding circular dependencies in Flex/AS3

I was looking for cycles in a directed graph in a task chart implementation I was doing for a client. My implementation of the Tarjan algorithm is hard coded for a linkage of task objects linked by constraints. I’d be interested to find out if anyone else has dug into this algorithm and gotten it to work.

package model.task {
  import ilog.gantt.TaskChart;


  public class Tarjan {
    private var index:int = 0;
    private var stack:Array = new Array();
    private var SCC:Array = new Array();
    public var taskChart:ilog.gantt.TaskChart;

    /**
     * N.B. Don't forget to reset the *.index = -1 after checking
     *
     * DJH 12/24/2009  This will only work for task nodes connected by constraints.  It does not traverse
     * the entire task hierachical data
     *
     * I don't fully understand but all nodes are treated as loops.  Look through the SCC
     * array for child arrays which with more than 1 node and those the the cycles.
     *
     */
    public function tarjan(task:Object /* node */ /*,  adjacencyList:Array*/  ):Array {
      trace("tarjan():: push task " + task.id);
      task.index = index;
      task.lowLink = index;
      index++;
      stack.push(task);
      var constraints:Array = taskChart.getFromConstraints(task);
      // Collect the successors
      if(constraints) {
        for each(var c:Object in constraints) {
          var toTask:Object = taskChart.getToTask(c);
          if(toTask == null) {
            // DJH 12/9/2009, fix the constraint does not chain to a successor, so ignore
            continue;
          }
          if(toTask.index == -1) {
            tarjan(toTask /*, adjacencyList*/ );
            task.lowLink = Math.min(task.lowLink, toTask.lowLink);
          } else if(stack.indexOf(toTask) >= 0) {
            task.lowLink = Math.min(task.lowLink, toTask.index);
          }
        }
      }
      if(task.lowLink == task.index) {
        var arr:Array = new Array();
        do {
          toTask = stack.pop();
          arr.push(toTask);
        } while(toTask != task)
        SCC.push(arr);
      }
      return SCC;
    }
  }
}