Intersection of two strings in Java

java algorithm intersection
Deepak picture Deepak · Dec 15, 2010 · Viewed 31.4k times · Source

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

Example: 

String s1 = new String("Sychelless");
String s2 = new String("Sydney");

Answer

Matthew Flaschen picture Matthew Flaschen · Dec 15, 2010

Using HashSet<Character>:

HashSet<Character> h1 = new HashSet<Character>(), h2 = new HashSet<Character>();
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.

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