56. Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

Example 1:

Input: [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:

Input: [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.

NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        sort(intervals.begin(),intervals.end(), [](vector<int> &a, vector<int> &b){return a[0]<b[0];});
        vector<vector<int>> res;
        if(intervals.empty())return res;
        res.push_back(intervals[0]);for(int i=1;i<intervals.size();++i)
        {
            if(res.back()[1]<intervals[i][0])
                res.push_back(intervals[i]);
            else
                res.back()[1]=max(res.back()[1],intervals[i][1]);
        }
        return res;
    }
};

先排序,按照interval的第一个元素,也就是开始值排序, 

比较每两个interval,  a的end和b的start