87-cases-by-type.apex

public Map<String, List<Case>> casesByType(List<Case> cases) {
    Map<String, List<Case>> result = new Map<String, List<Case>>();
    for (Case c : cases) {
        if (c.Type != null) {
            if (result.containsKey(c.Type)) {
                result.get(c.Type).add(c);
            }
            else {
                result.put(c.Type, new List<Case> { c });
            }
        }
    }
    return result;
}