MergeIntervals.java

package problems.medium;

import problems.utils.Interval;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * Created by sherxon on 1/28/17.
 */
public class MergeIntervals {
    public static void main(String[] args) {
        List<Interval> list = new ArrayList<>();
        list.add(new Interval(1, 4));
        list.add(new Interval(1, 4));

        merge(list);
        System.out.println(list);
    }

    static List<Interval> merge(List<Interval> intervals) {
        if (intervals.size() < 2) return intervals;
        intervals.sort((a, b) -> a.start - b.start);
        List<Interval> list = new ArrayList<>();
        list.add(intervals.get(0));
        for (int i = 1; i < intervals.size(); i++) {
            Interval prev = list.get(list.size() - 1);
            Interval current = intervals.get(i);
            if (current.start == prev.start) {
                if (current.end > prev.end)
                    prev.end = current.end;
            } else if (current.start <= prev.end) {
                if (current.end > prev.end)
                    prev.end = current.end;
            } else list.add(current);
        }

        return list;
    }

    static public List<Interval> merge2(List<Interval> intervals) {
        if (intervals.size() <= 1) return intervals;
        Collections.sort(intervals, (a, b) -> {
            int c = a.start - b.start;
            if (c == 0) c = a.end - b.end;
            return c;
        });
        List<Interval> list = new ArrayList<>();
        list.add(intervals.get(0));
        for (int i = 1; i < intervals.size(); i++) {
            Interval prev = list.get(list.size() - 1);
            Interval cur = intervals.get(i);
            if (prev.end >= cur.start && cur.end >= prev.end) {
                prev.end = cur.end;
            } else if (cur.start > prev.end) {
                list.add(cur);
            }
        }
        return list;
    }
}