Merge Intervals(lintcode 156)

Description

Given a collection of intervals, merge all overlapping intervals.

Example

Given intervals => merged intervals:

[                     [
  [1, 3],               [1, 6],
  [2, 6],      =>       [8, 10],
  [8, 10],              [15, 18]
  [15, 18]            ]
]

Interface

/**
 * Definition of Interval:
 * public class Interval {
 *     int start, end;
 *     Interval(int start, int end) {
 *         this.start = start;
 *         this.end = end;
 *     }
 */

class Solution {
    /**
     * @param intervals, a collection of intervals
     * @return: A new sorted interval list.
     */
    public List<Interval> merge(List<Interval> intervals) {
        // write your code here
    }

}

Solution

/**
 * Definition of Interval:
 * public class Interval {
 *     int start, end;
 *     Interval(int start, int end) {
 *         this.start = start;
 *         this.end = end;
 *     }
 */

class Solution {
    /**
     * @param intervals, a collection of intervals
     * @return: A new sorted interval list.
     */
    public List<Interval> merge(List<Interval> intervals) {
        // write your code here
        if (intervals == null || intervals.size() <= 1) {
            return intervals;
        }

        Collections.sort(intervals, new IntervalComparator());

        Interval last = intervals.get(0);
        List<Interval> results = new ArrayList<Interval>();

        for (int i = 1; i < intervals.size(); ++i) {
            Interval curr = intervals.get(i);
            if (last.end >= curr.start) {
                last.end = Math.max(last.end, curr.end);
            } else {
                results.add(last);
                last = curr;
            }
        }

        results.add(last);
        return results;
    }

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