Luxoft

Main.java

import java.util.*;

public class Main {
    public static void main(String[] args) {

        System.out.println("==== TASK 1 ====");
        Concatenation concatenation = new Concatenation();

        String word = "whataniceday";
        List<String> tokens = Arrays.asList("a", "what", "an", "nice", "day");
        System.out.println("WORD: '" + word +
                "'\tTOKENS: " + tokens + "\tRESULT: " +
                concatenation.validate(word, tokens));

        word = "dawhaty";
        tokens = Arrays.asList("a", "what", "an", "nice", "day");
        System.out.println("WORD: '" + word +
                "'\tTOKENS: " + tokens + "\tRESULT: " +
                concatenation.validate(word, tokens));

        word = "abc";
        tokens = Arrays.asList("a", "ab", "bc");
        System.out.println("WORD: '" + word +
                "'\tTOKENS: " + tokens + "\tRESULT: " +
                concatenation.validate(word, tokens));


        System.out.println("==== TASK 2 ====");
        Intervals merged = new Intervals();

        List<Interval> intervals = Arrays.asList(
                new Interval(2,6),
                new Interval(8,10),
                new Interval(1,3),
                new Interval(15,18),
                new Interval(18,21));
        System.out.println("INTERVALS: \t"+ intervals);
        System.out.println("MERGED: \t"+ merged.merge(intervals));

        intervals = Arrays.asList(
                new Interval(2,6),
                new Interval(8,10),
                new Interval(1,3),
                new Interval(15,18),
                new Interval(18,21),
                new Interval(5,15));
        System.out.println("INTERVALS: \t"+ intervals);
        System.out.println("MERGED: \t"+ merged.merge(intervals));

    }
}

class Concatenation {
    public boolean validate(String str, List<String> tokens) {
        String possibleWords = String.join("|", tokens);
        //Generate a regex string for string matching
        String regex = "^(" + possibleWords + ")+$";
        return str.matches(regex);
    }
}

class Interval{
    int start;
    int end;

    public Interval(int start, int end){
        this.start = start;
        this.end = end;
    }

    @Override
    public String toString() {
        return "[" + start + ", " + end + ']';
    }
}

class Intervals {
    public List<Interval> merge(List<Interval> intervals){
        Collections.sort(intervals, new IntervalComparator());

        LinkedList<Interval> result = new LinkedList<>();
        for (Interval interval : intervals) {
            // if the list is empty or didn overlap the last one
            if (result.isEmpty() || result.getLast().end < interval.start) {
                result.add(interval);
            }
            else {//if overlap -> merge
                result.getLast().end = Math.max(result.getLast().end, interval.end);
            }
        }
        return result;
    }

    private class IntervalComparator implements Comparator<Interval> {
        @Override
        public int compare(Interval a, Interval b) {
            return a.start < b.start ? -1 : a.start == b.start ? 0 : 1;
        }
    }
}