Intersection of two strings in Java

Question

Need a Java function to find intersection of two strings. i.e. characters common to the strings.

Example:

String s1 = new String(\"Sychelless\");
St         


        

Answer 1

Using HashSet:

HashSet h1 = new HashSet(), h2 = new HashSet();
for(int i = 0; i < s1.length(); i++)                                            
{
  h1.add(s1.charAt(i));
}
for(int i = 0; i < s2.length(); i++)
{
  h2.add(s2.charAt(i));
}
h1.retainAll(h2);
Character[] res = h1.toArray(new Character[0]);

This is O(m + n), which is asymptotically optimal.