maps exercise

public with sharing class MapExercises {
 // Given a list of Accounts, create and return a map where the KEY is the Account Id and the values are the Account
public static Map<Id, Account> getAccountMap(Account[] accs){
   Map<Id, Account> accounts = new Map<Id, Account>();
    for (Account ac : accs){
        accounts.put(ac.Id, ac);
    }  
    //System.debug('Get Account map from passed in data accounts === ', accs);
    return accounts;
}

// Given a list of Contacts, create and return a map where the KEY is an `Contact.Id` and the values are the related Account (`Contact.Account`)
public static Map<Id, Account> getAccountByContactId(Contact[] cts){
    Map<Id, Account> contacts = new Map<Id,Account>();

    for (Contact c : cts){
        contacts.put(c.Id, c.Account);
    }
    return contacts;
}


// Given a list of Contacts, create and return a 
//map where the KEY is an Account Id and the values are the list of contacts Associated to that account
// (via `contact.AccountId`)

public static Map<Id, Contact[]> groupContactsByAccountId(Contact[] contacts){
   Map<Id, List<Contact>> generatedMap = new Map<Id,List<Contact>>();

    for (Contact rc : contacts){
            //if generatedMap already contains the Account Id, add the contact to the list.  
        if (generatedMap.containsKey(rc.AccountId)){
            generatedMap.get(rc.AccountId).add(rc);
        } else { //Otherwise create a new list with the current contact
            generatedMap.put(rc.AccountId, new List<Contact>{rc});
        }
    }
    return generatedMap;
}


// Given a list of Accounts, create and return a map where the KEY is an `Account.Type` and the values the SUM of the account AnnualRevenue
public static Map<String, Decimal> getAccountRevenueBySum(Account[] accs){
    if (accs == null){
        return null;
    } else {
    Map<String,Decimal> accountMap = new Map<String,Decimal>();
    for (Account a : accs){
        if (accountMap.containsKey(a.Type)){
            accountMap.put(a.Type, accountMap.get(a.Type) + a.AnnualRevenue);
        } else {
            accountMap.put(a.Type, a.AnnualRevenue);
        }
    }
    return accountMap;
    }
}
}