how to remove duplicate results generating from hashmap

user_3937767 0
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I was given a problem - there is a box containing label and has value in it. for example - box with label 'a' contains value 2, box with label 'b' contains value 7 etc. I was asked to find the pairs that adds to sum 10. I wrote below code to find the pair using hashmap. But it contains same result twice with only difference of position of letter. For example - (a,e) is same as (e,a) How can I keep/print only the unique pair?

Below is my code : 

 public class BoxValue {

   public void pair()
    {
      int sum = 10;
      HashMap<Integer, Character> m = new HashMap<Integer, Character>();

      m.put(2, 'a');
      m.put(7, 'b');
      m.put(4, 'c');
      m.put(3, 'd');
      m.put(8, 'e');
      m.put(6, 'f');

    Set<Integer> s = m.keySet();       

     for(Integer in : s)
      {
        if(m.containsKey(sum-in))                     
         System.out.println(m.get(in)+","+m.get(sum-in));         
      }
   }


 public static void main(String[] args) {

    BoxValue bv = new BoxValue();
    bv.pair();
  }

}
hashmap java
2 Answers

I would just use a Set to keep track of which complements you've already seen:

Set<Integer> seen = new HashSet<>();        
for (Integer in : m.keySet())
{
    if(m.containsKey(sum-in) && !seen.contains(in))
    {
        System.out.println(m.get(in) + "," + m.get(sum-in));
        seen.add(sum-in);
    }
}

You can do it without any additional storage if you're able to modify the map, at the loss of some clarity:

for (Integer in : m.keySet())
{
    if(m.containsKey(sum-in) && m.get(in) != null)
    {
        System.out.println(m.get(in) + "," + m.get(sum-in));
        m.put(sum-in, null);
    }
}

Output:

a,e
d,b
c,f
user_64388190

You can use a map for keys

List<Integer> s = new ArrayList<>(m.keySet()); // Create a key list
HashMap<Integer, Boolean> pos = new HashMap<Integer, Boolean>(); // Map for used key
for (int i = 0; i < s.size(); i++) {
  if (m.containsKey(sum - s.get(i)) && !pos.containsKey(sum - s.get(i)))
    System.out.println(m.get(s.get(i)) + "," + m.get(sum - s.get(i)));
  pos.put(s.get(i), true); // Update map
}
user_42073060
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