#Trailhead612 debatiendo

Hi Deepak - for grouping, Map<Key, List<T>> is almost always the right call. List<List<T>> is rarely right for grouping because you lose the key (no O(1) lookup - you would have to scan to find a group). 

When to prefer each: 

- Map<Key, List<T>>: anytime you group BY something, e.g. Map<Id, List<Contact>> keyed by AccountId. O(1) lookup, keys auto-dedup, and it is the bulkification backbone in triggers. 

- List<List<T>>: only when there is no meaningful key and the split is positional - fixed-size chunks for a callout that takes N records per request, or partitioning work across async jobs. You just iterate the sublists, never look up by key. 

Governor / performance: 

- The limit that actually bites is HEAP (6 MB sync / 12 MB async), driven by how many records you hold in memory, not the collection shape. Map's key overhead is negligible. 

- Map's real win is avoiding nested loops: correlating two lists via a Map is O(n); scanning a List<List<>> to find a group re-introduces O(n-squared). That is the real consideration. 

- Neither changes SOQL/DML limits - those depend on bulkifying, which you do either way. 

Pattern I use for grouping SOQL results: 

Map<Id, List<Contact>> byAcct = new Map<Id, List<Contact>>(); 

for (Contact c : [SELECT Id, AccountId FROM Contact]) { 

  if (!byAcct.containsKey(c.AccountId)) byAcct.put(c.AccountId, new List<Contact>()); 

  byAcct.get(c.AccountId).add(c); 

} 

Two more: for a true parent-child group, a subquery like [SELECT Id, (SELECT Id FROM Contacts) FROM Account] groups it at the query level - often cleaner. And for two dimensions, Map<Key1, Map<Key2, List<T>>> stays keyed and O(1). 

Net: default to Map<Key, List<T>> for grouping; reach for List<List<T>> only for keyless chunking. 

If this helps, please mark it as the Best Answer so it helps the next person - thanks :)

@Sahil Gupta

 is cancel option showing besides Lightning Login in Brochan's user record? 

If this is also the same, then I think the setup is correct. Not sure why the challenge is failing. 

Last option would be to sign up for a new org from the 

link -> Change Brochan's email to your email and also set the password -> Enable the Lightning Login option from setup -> Create the two PS as asked in the module: Lightning Login User 

MFA Authorization for Break Glass Admin 

-> Assign both the PS to Brochan -> Enroll Brochan to Lightning Login and login as passwordless 

Try to validate the challenge again. Just validate the specific module where you are stuck, no need to validate the previous steps which are passed already. These are the steps I followed yesterday and it passed the challenge. Good luck. 

Thanks. 

Abhishek