swap keys and duplicate values in hashmap

Anonymous User 2018 22 Apr 2015

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?

Ask by Anonymous User

Updated 22 Apr 2015

1 Answers

Anonymous User 22 Apr 2015

Finally after a lot of research i have done it

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

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