56. Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

Example 1:

Input:
 [[1,3],[2,6],[8,10],[15,18]]

Output:
 [[1,6],[8,10],[15,18]]

Explanation:
 Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:

Input:
 [[1,4],[4,5]]

Output:
 [[1,5]]

Explanation:
 Intervals [1,4] and [4,5] are considerred overlapping.

Solution

(1) Java

/**
 * 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) {
        List<Interval> rst = new ArrayList<>();
        if (intervals == null || intervals.size() <= 1) {
            return intervals;
        }
        Collections.sort(intervals, (Interval i1, Interval i2)->i1.start-i2.start);
        int end = 0;
        for (Interval iv : intervals) {
            if (rst.size() == 0) {
                rst.add(iv);
                end = iv.end;
            } else {
                if (iv.start <= end) {
                    Interval iv2 = rst.remove(rst.size()-1);
                    iv2.end = Math.max(iv2.end, iv.end);
                    rst.add(iv2);
                    end = iv2.end;
                } else {
                    rst.add(iv);
                    end = iv.end;
                }
            }
        }
        return rst;
    }
}

(2) Python

# Definition for an interval.
# class Interval:
#     def __init__(self, s=0, e=0):
#         self.start = s
#         self.end = e

class Solution:
    def merge(self, intervals):
        """
        :type intervals: List[Interval]
        :rtype: List[Interval]
        """
        if not intervals:
            return intervals
        intervals.sort(key=lambda x: x.start)
        rst = []
        for interval in intervals:
            if not rst or rst[-1].end < interval.start:
                rst.append(interval)
            else:
                rst[-1].end = interval.end if interval.end > rst[-1].end else rst[-1].end
        return rst

(3) Scala