超出Apex CPU时间限制

Question

我有这个递归查找以获取销售代表所属的地区列表 - 问题是我遇到了“太多CPU时间”调控器限制。关于如何重新编写它以使它不这样做的任何建议？

public List<string> getHeirarchy() {
    List<Territory> territories = [SELECT Id, Custom_External_TerritoryId__c, ExternalParentTerritoryId__c FROM Territory];
    return getParentAndChildren(getTerritory(), territories);
}

public Set<string> getChildren(string parent, List<Territory> territories) {
    Set<string> subset = new Set<string>();
    for(Territory t : territories) {
       if (t.ExternalParentTerritoryId__c == 'US-'+parent) {
           subset.add(t.Custom_External_TerritoryId__c.SUBSTRING(3));
       }
    }

    return subset;
}

public List<string> getParentAndChildren(string parent, List<Territory> territories) {
    Set<string> collection = new Set<string>();

    Set<string> children = getChildren(parent, territories);
    if(children.size() > 0) {
        for(string child : children) {
            collection.addAll(getParentAndChildren(child, territories));
        }
    }
    collection.add(parent);

    List<string> sorted = new List<string>(collection);
    //sorted.sort();
    return sorted;
}