056.Merge Intervals

Posted on | In

Solution 1: accepted 28ms 59%

Time: O(2n)
Space: O(n) 

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class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        if (intervals.size() < 2) 
            return intervals;
        List<Interval> result = new ArrayList<>();
        Collections.sort(intervals, new IntervalComparator());
        
        Interval temp = new Interval();
        for (int i = 0; i < intervals.size() - 1; i++) {
            if (intervals.get(i).end < intervals.get(i + 1).start) {
                result.add(intervals.get(i));
            } else if (intervals.get(i).start == intervals.get(i + 1).start) {
                intervals.get(i + 1).end = Math.max(intervals.get(i).end, intervals.get(i + 1).end);
            } else {
                intervals.get(i + 1).start = intervals.get(i).start;
                intervals.get(i + 1).end = Math.max(intervals.get(i).end, intervals.get(i + 1).end);
            }
        }
        result.add(intervals.get(intervals.size() - 1));
        return result;
    }
    
    private class IntervalComparator implements Comparator<Interval> {
        
        public int compare(Interval a, Interval b) {
            if (a.start < b.start)
                return -1;
            else if (a.start > b.start)
                return 1;
            else 
                return 0;
        }
    } 
}
Simplified
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class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        if (intervals.size() < 2) 
            return intervals;
        List<Interval> result = new ArrayList<>();
        Collections.sort(intervals, new Comparator<Interval>() {
            public int compare(Interval a, Interval b) {
                return a.start - b.start;
        }
        });
        
        Interval temp = new Interval();
        for (int i = 0; i < intervals.size() - 1; i++) {
            Interval current = intervals.get(i);
            Interval next = intervals.get(i + 1);
            if (current.end < next.start) {
                result.add(current);
            } else {
                next.start = current.start;
                next.end = Math.max(current.end, next.end);
            } 
        }
        result.add(intervals.get(intervals.size() - 1));
        return result;
    } 
}