56. Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

For example,
Given [1,3],[2,6],[8,10],[15,18],
return [1,6],[8,10],[15,18].

Solution：

思路：
Time Complexity: O(N) Space Complexity: O(N)

Solution Code：

/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        if (intervals.size() <= 1)
            return intervals;

        // Sort by ascending starting point using an anonymous Comparator
        intervals.sort((i1, i2) -> i1.start - i2.start);

        List<Interval> result = new LinkedList<Interval>();
        int start = intervals.get(0).start;
        int end = intervals.get(0).end;

        for (Interval interval : intervals) {
            if (interval.start <= end) // Overlapping intervals, move the end if needed
                end = Math.max(end, interval.end);
            else {                     // Disjoint intervals, add the previous one and reset bounds
                result.add(new Interval(start, end));
                start = interval.start;
                end = interval.end;
            }
        }

        // Add the last interval
        result.add(new Interval(start, end));
        return result;
    }
}