【LeetCode】56. Merge Intervals

問題描述

https://leetcode.com/problems/merge-intervals/#/description

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].

數軸覆蓋問題。

算法

將各條線段的start按從小到大排序，然後依次比較每條線段的end，看是否被前一段覆蓋即可。

代碼

public List<Interval> merge(List<Interval> intervals) {
            List<Interval> res = new ArrayList<>();
            if(intervals == null || intervals.isEmpty()) return res;
            Collections.sort(intervals, new Comparator<Interval>(){

                @Override
                public int compare(Interval a, Interval b) {
                    if(a.start < b.start) {
                        return -1;
                    } else if(a.start > b.start) {
                        return 1;
                    }
                    return 0;
                }
            });
            int start=intervals.get(0).start, end=intervals.get(0).end;
            for(Interval it:intervals) {
                if(it.start <= end) {
                    end = Math.max(it.end, end);
                } else {
                    res.add(new Interval(start, end));
                    start = it.start;
                    end = it.end;
                }
            }
            res.add(new Interval(start, end));
            return res;
        }

LeetCode解題代碼倉庫：https://github.com/zgljl2012/leetcode-java