Question

Write a method List duplicates(List-Doubles input) that returns a List af all duplicates in the input List. You may assume thai each elemert occurs either once or twicc. The expected runtime nust be Oo) whece n is the number a elements (even if the input is a Linkodl ist, the runtime should still he n) ino credit for slower runtimes, so you cancsot sort the input). (12 point) Examples: input 13, 4,4 retum [4 input 13.7, 4, 7,3] rctum 17, 3] ListくDouble) duplicates(し1st

Answer 1

import java.util.*;

public class FindDuplicatesInList {

    List<Double> duplicates(List<Double> input) {
        List<Double> duplicates = new ArrayList<>();
        Map<Double, Integer> map = new HashMap<>();
        Iterator<Double> iterator = input.iterator();
        Double number;
        while (iterator.hasNext()) {
            number = iterator.next();
            if (map.containsKey(number)) {
                duplicates.add(number);
            } else {
                map.put(number, 0);
            }
        }
        return duplicates;
    }

    public static void main(String[] args) {
        LinkedList<Double> numbers = new LinkedList<>();
        numbers.add(3.0);
        numbers.add(4.0);
        numbers.add(4.0);

        System.out.println(new FindDuplicatesInList().duplicates(numbers));
    }
}