LeetCoe 56. Merge Intervals

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Description

https://leetcode.com/problems/merge-intervals/
合并区间

Solving Ideas

https://leetcode.com/problems/merge-intervals/solution/

按区间下限的大小对区间进行排序，然后再对区间进行合并

时间复杂度： $O(nlog(n))$
空间复杂度： $O(1)$

Solution

class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        if (intervals == null) return null;
        List<Interval> res = new ArrayList<>();
        if (intervals.size() == 0) return res;
        
        intervals.sort(new Comparator<Interval>() {
            @Override
            public int compare(Interval o1, Interval o2) {
                return Integer.compare(o1.start, o2.start);
            }
        });

        int lower = intervals.get(0).start;
        int upper = intervals.get(0).end;

        for (int i = 1; i < intervals.size(); i++) {
            Interval tmp = intervals.get(i);
            if (tmp.start <= upper) {
                upper = Math.max(upper, tmp.end);
            } else {
                res.add(new Interval(lower, upper));
                lower = tmp.start;
                upper = tmp.end;
            }
        }

        res.add(new Interval(lower, upper));
        return res;
    }
}