Code used in set to list and list to set conversion tutorial on SFDC Stop https://youtu.be/ArSOAxTOuHo

settolistandlisttoset.cls

Convert Set to List
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Set<Integer> numbers = new Set<Integer>{30,30,30,20,20,10,40,40};
System.debug('Initial Set -> ' + numbers);

List<Integer> numbersList = new List<Integer>(numbers);
System.debug('List from Set -> ' + numbersList);

System.debug('Number at index 2 = ' + numbersList[2]);

Convert List to Set
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List<Integer> numbersList = new List<Integer>{30,30,30,20,20,10,40,40};
System.debug('Initial List -> ' + numbersList);

Set<Integer> numbers = new Set<Integer>(numbersList);
System.debug('Set from List -> ' + numbers);