Few Apex Scenario Based Programming Questions

Recently at one of the local Hackathon I came across some scenario based Apex programming questions and I thought I would go ahead and blog on them. Below are three scenarios on which we are going to write some Apex code!

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Scenario 1: Create a Method which accepts List of String and returns a Map with count on how many times a specific value is repeated in a given List. Example:- List<'A', 'B', 'A', 'C', 'B', 'A'> should result in "{A=3, B=2, C=1}"

Approached Solution: Below is my Apex class with a method to accept List and returns a Map.

/*
* Purpose: Hackathon Programming Scenarios
* 
* Developer: HackathonDev
*/

public class HackathoScenarios {
    // Method to return a map with string occurence count that was passed in a list
    public static Map<String, Integer> scenario1(List<String> lstStrng) {
        Map<String, Integer> mapVals = new Map<String, Integer>();
        
        for (String s: lstStrng) {            
            if (mapVals.containsKey(s)) {
                mapVals.put(s, mapVals.get(s)+1);
            } else {
                mapVals.put(s, 1);
            }
        }
        return mapVals;
    }
}

When I use below sample code block to execute from my execute anonymous Dev Console window, I see below results.
Sample Code:

List<String> lstS = new List<String>{'A', 'B', 'A', 'C', 'B', 'A', 'Test', 'Testing', 'A', 'Test'};
Map<String, Integer> mapRslts = HackathoScenarios.scenario1(lstS);
System.debug('************' + mapRslts);

Debug Log Result:

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Scenario 2: Create a Method which accepts List of records to update and return List of all record id's that failed to update.

Approached Solution: Below is my Apex class with a method to accept List of sObjects and returns a List of String with failed record Id's. Here I tried to use "SaveResults" class to get update results.

/*
* Purpose: Hackathon Programming Scenarios
* 
* Developer: HackathonDev
*/

public class HackathoScenarios {
    // Method to return list of Id's that had exception while updating records
    public static List<String> scenario2 (List<sObject> lstRecords) {
        List<String> lstRcdIds = new List<String>();
        Map<String, String> mapRcdIds = new Map<String, String>();
        
        try {
            Database.SaveResult[] srList = Database.update(lstRecords, false);
            for (Database.SaveResult sr : srList) {
                if (sr.isSuccess()) {                   
                    // Add record id to the map
                    mapRcdIds.put(sr.getId(), sr.getId());
                    System.debug('************Success Record Id: ' + sr.getId());
                } else {                   
                    // Debug failed record id and this will result in 'null'
                    System.debug('************Failed Record Id: ' + sr.getId());                    
                }
            }
        } catch (exception e) {
            lstRcdIds.add('There is an exception while updating records: ' + e.getMessage());
        }
        
        // Loop through the initial list of records to separate failed record id and add them to a list
        for (sObject s: lstRecords) {
            if (!mapRcdIds.containsKey(s.Id)) {
                lstRcdIds.add(s.Id);
            }
        }
        return lstRcdIds;
    }
}

I created a Validation rule on Account to require Phone number on updates and When I use below sample code block to execute from my execute anonymous Dev Console window, I see below results with failed record Id's List.
Sample Code:

List<Account> lstAccnts = [Select Id, Name From Account Limit 22];

for (Account acc: lstAccnts) {
    acc.Name = acc.Name + 'Testing';
}

List<String> lstFailedIds = HackathoScenarios.scenario2(lstAccnts);

System.debug('************' + lstFailedIds);

Debug Log Result:

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Scenario 3: Create a Method to Encrypt/Decrypt using Crypto class.

Approached Solution: Below is my Apex class with a method to accept String value and Encrypt/Decrypt using Crypto class available method.

/*
* Purpose: Hackathon Programming Scenarios
* 
* Developer: HackathonDev
*/

public class HackathoScenarios {
    // Method to Encrypt/Decrypt using Crypto class methods
    public static void scenario3(String urlParam) {
        // Generate crypto key
        Blob cryptoKey = Crypto.generateAesKey(256);        
        // Generate initialization vector - Make sure this is always 16 bytes!
        Blob initialVec = Blob.valueOf('abcdefghijklmnop');
        
        // Convert string to blob
        Blob data = Blob.valueOf(urlParam);
        
        // Encrypt using Crypto Encrypt method
        Blob encryptedData =  Crypto.encrypt('AES256', cryptoKey, initialVec, data);
        
        System.debug('************Encrypted Code: ' + encryptedData);
        
        // Decrypt using Crypto Decrypt method
        Blob decryptedData = Crypto.decrypt('AES256', cryptoKey, initialVec, encryptedData);
        
        System.debug('************Decrypted Code: ' + decryptedData);
        
        // Obtain Decrypt value as String
        String decryptedDataString = decryptedData.toString();
        
        System.debug('************Decrypted Code: ' + decryptedDataString);
    }
}

Use below sample code block to execute from my execute anonymous Dev Console window
Sample Code:

String s = 'https://reddydev2018-dev-ed.my.salesforce.com/_ui/common/apex/debug/ApexExecAnon';
HackathoScenarios.scenario3(s);

Debug Log Result:

Thank you!