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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.util.function.*;
  5. import java.util.stream.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	public static void main (String[] args) throws java.lang.Exception
  11. 	{
  12. 		Map<String, List<String>> groupsMap = new HashMap<>();
  13. 		groupsMap.put("1", new ArrayList<>());
  14. 		groupsMap.get("1").add("Jeff");
  15. 		groupsMap.get("1").add("Bob");
  16. 		groupsMap.put("2", new ArrayList<>());
  17. 		groupsMap.get("2").add("Jeff");
  18.  
  19. 		String socialButterfly = groupsMap.values()
  20.             .stream()
  21.             .flatMap(Collection::stream)
  22.             .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
  23.             .entrySet()
  24.             .stream()
  25.             .max(Map.Entry.comparingByValue())
  26.             .get()
  27.             .getKey();
  28.         System.out.println(socialButterfly);
  29. 	}
  30. }
Success #stdin #stdout 0.25s 320960KB
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Standard input is empty
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Jeff
https://ideone.com/FiBzL9
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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