uncommon - Intersection of two strings in Java




union of two strings (7)

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");

Optimized solution:

public static String twoStrings(String s1, String s2){

    HashSet<Character> stringOne =  new HashSet<Character>(), stringTwo = new HashSet<Character>();  
    int stringOneLength = s1.length();
    int stringTwoLength = s2.length();
    for(int i=0; i<stringOneLength || i<stringTwoLength; i++) {
        if(i < stringOneLength)
            stringOne.add(s1.charAt(i));
        if(i < stringTwoLength)
            stringTwo.add(s2.charAt(i));
    }
    stringOne.retainAll(stringTwo);

    return stringOne.toString();
}

By means of Guava this task seems much easier:

String s1 = new String("Sychelless");
String s2 = new String("Sydney");
Set<String> setA = Sets.newHashSet(Splitter.fixedLength(1).split(s1));
Set<String> setB = Sets.newHashSet(Splitter.fixedLength(1).split(s2));
Sets.intersection(setA, setB);


I have used TreeSet. And retainAll() in TreeSet to get matched elements.

Oracle Doc:

retainAll(Collection<?> c)

Retains only the elements in this set that are contained in the specified collection (optional operation).

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

Set<Character> firstSet = new TreeSet<Character>();
for(int i = 0; i < s1.length(); i++) {
    firstSet.add(s1.charAt(i));
}

Set<Character> anotherSet = new TreeSet<Character>();
for(int i = 0; i < s2.length(); i++) {
    anotherSet.add(s2.charAt(i));
}

firstSet.retainAll(anotherSet);
System.out.println("Matched characters are " + firstSet.toString());//print common strings

//output > Matched characters are [S, e, y]

More detail on saugata's response (appeared while I was writing this): -

public static void main(String[] args) {
    String s1 = "Seychelles";
    String s2 = "Sydney";
    Set<Character> ss1 = toSet(s1);
    ss1.retainAll(toSet(s2));
    System.out.println(ss1);
}

public static Set<Character> toSet(String s) {
    Set<Character> ss = new HashSet<Character>(s.length());
    for (char c : s.toCharArray())
        ss.add(Character.valueOf(c));
    return ss;
}

Most basic approach:

String wordA = "Sychelless";  
String wordB = "Sydney";  
String common = "";  

for(int i=0;i<wordA.length();i++){  
    for(int j=0;j<wordB.length();j++){  
        if(wordA.charAt(i)==wordB.charAt(j)){  
            common += wordA.charAt(i)+" ";  
            break;
        }  
    }  
}  
System.out.println("common is: "+common);  

s1.contains(s2) returns true;
s1.indexOf(s2) returns 0. 
s1.indexOf("foo") returns -1

For more sophisticated cases use class Pattern.





intersection