swap keys and duplicate values in hashmap

Hey Everyone,

I have interesting question on hash map and it says :

I have a hash map with values : {"1-a","2-a","3-b","4-b"}

Keys Values

1 a

2 a

3 b

4 b

I need to swap the key values with losing the data , means the new hash map should be :

Keys Values

a 1,2

b 3,4

Can anyone suggest me the way to do this?

java

Updated on 22-Apr-2015

Map<String, Set<String> > newmap = new HashMap<String, Set<String> >();
map.put("1", "a");
map.put("2", "a");
map.put("3", "b");
map.put("4", "b");
System.out.println("before Reversing");
for (Map.Entry<String, String> entry : map.entrySet())
{
System.out.println("The key ::"+entry.getKey()+":: The value"+entry.getValue());
}
for (Map.Entry<String, String> entry : map.entrySet())
{
String oldVal = entry.getValue();
String oldKey = entry.getKey();
Set<String> newVal = null;
if (newmap.containsKey(oldVal))
{
newVal = newmap.get(oldVal);
newVal.add(oldKey);
}
else
{
newVal= new HashSet<>();
newVal.add(oldKey);
}
newmap.put(oldVal, newVal);
}
System.out.println("After Reversing");
for (Map.Entry<String, Set<String>> entry : newmap.entrySet())
{
System.out.print("The key ::"+entry.getKey()+":: The value"+entry.getValue());
}
}
}

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swap keys and duplicate values in hashmap

Anonymous User

1 Answers

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