思路，先按照結構體中start進行排序，然後遍歷比較前後項是否有重合。

第一次用到三參數形式的sort()，第三個參數的bool函數要寫到類外才通過。

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */
   bool cmp(Interval a, Interval b){
        
 
return a.start < b.start;
    }
class Solution {
public:

    
    vector<Interval> merge(vector<Interval>& intervals) {
        const int Size = intervals.size();
        if(Size <= 1) return intervals;
        vector<Interval> ans;
        Interval temp;
        vector
 
<bool>visited(Size,false);
        sort(intervals.begin(), intervals.end(),cmp);
        temp = intervals[0];
        for(int i = 0; i < Size - 1; i++)
        {
            if((visited[i] &&temp.end >= intervals[i + 1].start) || intervals[i].end >= intervals[i + 1].start){
                
 
int m = min(intervals[i].start, intervals[i + 1].start);
                int M = max(intervals[i].end, intervals[i + 1].end);
                temp.start = min(m, temp.start);
                temp.end = max(M, temp.end);
                visited[i + 1] = true;
                visited[i] = true;
            }
            else{
                if(visited[i]) ans.push_back(temp);
                else ans.push_back(intervals[i]);
                temp = intervals[i + 1];
            }
        }
        if(visited[Size - 1]) ans.push_back(temp);
                else ans.push_back(intervals[Size - 1]);
        return ans;
    }
};

leetcode個人題解——#56 Merge Intervals