CODEWITHSUNDEEP
javastringarraylistequalscontains
Jobin
Jobin

Reputation: 1361

Efficient way to find multiple objects in Arraylist

I have to check whether an arraylist contains any of the value passed through an object.

Consider an arraylist with values "abc", "jkl","def", "ghi". And String check="abc,ghi"

We have to check whether any of the value in string (abc or ghi) is present in the arraylist and we can stop checking when a match is found.

Traditionally, we can split the String check with comma and use arraylist.contains() in iteration for each comma separated values.

But this is time consuming. Is there any better way to do this check.

Upvotes: 1

Views: 6424

Answers (3)

Kenster
Kenster

Reputation: 25390

This is still O(n), but you could build a set from the search strings and just iterate over the list once:

HashSet<String> checks = new HashSet<String>();
checks.addAll(Arrays.asList(check.split(",")));
for (String item : arraylist) {
    if (checks.contains(item)) {
        // Found one
    }
}

Upvotes: 0

Mena
Mena

Reputation: 48404

One way would be to use the retainAll method and Sets.

Example

// note an additional "ghi" here
List<String> original = new ArrayList<String>(Arrays.asList(new String[]{"abc", "jkl","def", "ghi", "ghi"}));
Set<String> clone = new HashSet<String>(original);
Set<String> control = new HashSet<String>(Arrays.asList(new String[]{"abc","ghi"}));
clone.retainAll(control);
System.out.println(clone.equals(control));

Output

true

Upvotes: 2

cadrian
cadrian

Reputation: 7376

You could transform check into a regexp and loop only once through the ArrayList.

String check = "abc,ghi";
Pattern p = Pattern.compile("(" + check.replace(',', '|') + ")");
List<String> list = Arrays.asList(new String[] { "abc", "jkl", "def", "ghi" });
for (String element : list) {
    if (p.matcher(element).matches()) {
        System.out.println("match: " + element);
    }
}

Upvotes: 0

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