LeetCode 352. Data Stream as Disjoint Intervals

原题链接在这里：https://leetcode.com/problems/data-stream-as-disjoint-intervals/description/

题目：

Given a data stream input of non-negative integers a1, a2, ..., an, ..., summarize the numbers seen so far as a list of disjoint intervals.

For example, suppose the integers from the data stream are 1, 3, 7, 2, 6, ..., then the summary will be:

[1, 1]
[1, 1], [3, 3]
[1, 1], [3, 3], [7, 7]
[1, 3], [7, 7]
[1, 3], [6, 7]

Follow up:
What if there are lots of merges and the number of disjoint intervals are small compared to the data stream's size?

题解：

利用TreeMap<Integert, Interval> tm来保存每段Interval的start 和 Interval本身的对应关系. 

新值进来就看能不能连上已有的Interval.

Time Complexity: addNum, O(logn). getIntervals, O(n).

Space: O(n).

AC 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 SummaryRanges {
    TreeMap<Integer, Interval> tm;
    /** Initialize your data structure here. */
    public SummaryRanges() {
        tm = new TreeMap<Integer, Interval>();
    }
    
    public void addNum(int val) {
        if(tm.containsKey(val)){
            return;
        }
        Integer l = tm.lowerKey(val);
        Integer r = tm.higherKey(val);
        if(l!=null && r!=null && tm.get(l).end+1==val && val+1==r){
            tm.get(l).end = tm.get(r).end;
            tm.remove(r);
        }else if(l!=null && tm.get(l).end+1>=val){
            tm.get(l).end = Math.max(val, tm.get(l).end);
        }else if(r!=null && val+1==r){
            tm.put(val, new Interval(val, tm.get(r).end));
            tm.remove(r);
        }else{
            tm.put(val, new Interval(val, val));
        }
    }
    
    public List<Interval> getIntervals() {
        return new ArrayList<Interval>(tm.values());
    }
}

/**
 * Your SummaryRanges object will be instantiated and called as such:
 * SummaryRanges obj = new SummaryRanges();
 * obj.addNum(val);
 * List<Interval> param_2 = obj.getIntervals();
 */

 类似Missing Ranges, Summary Ranges.