Merge Intervals

Problem

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]            ]
]

Challenge

O(n log n) time and O(1) extra space.

Code - Java

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

class Solution {
/**
* @param intervals: Sorted interval list.
* @return: A new sorted interval list.
*/
public List<Interval> merge(List<Interval> intervals) {
Collections.sort(intervals, new Comparator<Interval>() {
public int compare(Interval a, Interval b) {
return a.start - b.start;
}
});

List<Interval> result = new ArrayList<Interval>();

int size = intervals.size();
if (size == 1) {
return intervals;
}
for (int i = 1; i < size; i++) {
if (intervals.get(i - 1).end >= intervals.get(i).start) {
intervals.get(i).start = intervals.get(i - 1).start;
intervals.get(i).end = Math.max(intervals.get(i).end, intervals.get(i - 1).end);

} else {
}