352. Data Stream as Disjoint Intervals

题目链接: https://leetcode.com/problems/data-stream-as-disjoint-intervals/

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?

解析：

题目的意思是新加进来的数字如果遇到连续区间就合并

方法一用vector

/**
 * 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:
    void addNum(int val) {
        auto Cmp = [](Interval a, Interval b) { return a.start < b.start; };　　
        auto it = lower_bound(vec.begin(), vec.end(), Interval(val, val), Cmp);
        int start = val, end = val;
        if(it != vec.begin() && (it-1)->end+1 >= val) it--;
        while(it != vec.end() && val+1 >= it->start && val-1 <= it->end)
        {
            start = min(start, it->start);
            end = max(end, it->end);
            it = vec.erase(it);
        }
        vec.insert(it,Interval(start, end));
    }
    
    vector<Interval> getIntervals() {
        return vec;
    }
private:
    vector<Interval> vec;
};

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

注意：

auto Cmp = [](Interval a, Interval b) { return a.start < b.start; };

这里实际上用的是一个lambda表达式

auto it = lower_bound(vec.begin(), vec.end(), Interval(val, val), Cmp);

这样代码用了C11中的auto，根据初始化的值的类型来推断变量类型的功能，这里it的类型实际上是vector<Interval>::iterator

方法二用set

/**
 * 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:
    void addNum(int val) {
        auto Cmp = [](Interval a, Interval b) { return a.start < b.start; };
        auto it = lower_bound(vec.begin(), vec.end(), Interval(val, val), Cmp);
        int start = val, end = val;
        if(it != vec.begin() && (it-1)->end+1 >= val) it--;
        while(it != vec.end() && val+1 >= it->start && val-1 <= it->end)
        {
            start = min(start, it->start);
            end = max(end, it->end);
            it = vec.erase(it);
        }
        vec.insert(it,Interval(start, end));
    }
    
    vector<Interval> getIntervals() {
        return vec;
    }
private:
    vector<Interval> vec;
};

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