[Leetcode] 352. Data Stream as Disjoint Intervals 解题报告

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?

思路：

由于是数据流，所以我们无法提前对它们进行排序。这里的关键在于新加入一个数字之后，如何对现有的Intervals进行合并或者添加。我们的实现方法是维护一个Intervals的set。在新加入一个数字之后，我们首先在set中找到第一个比它大的Interval，然后从它的 前一个Interval开始进行合并。在合并过程中我们采取的策略是，一旦能够和下一个Interval连接上，就删掉下一个Interval。直到无法连接的时候，我们插入合并后的Interval。

代码：

/** * Definition for an interval. * struct Interval { *     int start; *     int end; *     Interval() : start(0), end(0) {} *     Interval(int s, int e) : start(s), end(e) {} * }; */class SummaryRanges {public:    /** Initialize your data structure here. */    SummaryRanges() {            }        void addNum(int val) {        auto it = intervals.lower_bound(Interval(val, val));        int start = val, end = val;          if(it != intervals.begin()) {            --it;            if(it->end + 1 < val) {                ++it;            }        }        while(it != intervals.end() && val + 1 >= it->start && val - 1 <= it->end) {              start = min(start, it->start);              end = max(end, it->end);              it = intervals.erase(it);         }          intervals.insert(it, Interval(start, end));    }        vector<Interval> getIntervals() {        return vector<Interval>(intervals.begin(), intervals.end());    }private:    struct IntervalCompare {        bool operator() (const Interval &a, const Interval &b) {            if(a.start < b.start)                return true;            else if(a.start > b.start)                return false;            else                return a.end < b.end;        }    };    set<Interval, IntervalCompare> intervals;};/** * Your SummaryRanges object will be instantiated and called as such: * SummaryRanges obj = new SummaryRanges(); * obj.addNum(val); * vector<Interval> param_2 = obj.getIntervals(); */