352. Data Stream as Disjoint Intervals

最新推荐文章于 2022-07-14 20:57:05 发布

转载最新推荐文章于 2022-07-14 20:57:05 发布 · 70 阅读

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原文链接：https://segmentfault.com/a/1190000006174763

本文介绍了一种使用TreeMap实现的数据结构来高效处理连续输入的非负整数流，并将其总结为不相交区间的方法。特别地，讨论了当数据流中存在大量合并操作且不相交区间数量远小于数据流大小的情况下的优化方案。

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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?

解答：
这题用Maptree会通过map.lowerKey, map.higherKey很快定位到当前数所处在哪两个interval之间，从而进行高效的比较与合并。

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

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