leetcode_question_57 Insert Interval

Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary).

You may assume that the intervals were initially sorted according to their start times.

Example 1:
Given intervals [1,3],[6,9], insert and merge [2,5] in as [1,5],[6,9].

Example 2:
Given [1,2],[3,5],[6,7],[8,10],[12,16], insert and merge [4,9] in as [1,2],[3,10],[12,16].

This is because the new interval [4,9] overlaps with [3,5],[6,7],[8,10].

/**
 * 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 Solution {
public:
    vector<Interval> insert(vector<Interval> &intervals, Interval newInterval) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<Interval>::iterator itstart=intervals.begin();
    	for(; itstart!=intervals.end(); ++itstart)
			if((*itstart).start <= newInterval.start && newInterval.start <= (*itstart).end)
				break;
		vector<Interval>::iterator itend=intervals.begin();
		for(; itend!=intervals.end(); ++itend)
    		if((*itend).start <= newInterval.end && newInterval.end <= (*itend).end)
				break;
		if(itstart!=intervals.end() && itend!=intervals.end())
		{
			if(itstart != itend)
			{
				(*itstart).end = (*itend).end;
                int tmp = (*itstart).end;
    			itstart++;
				while(itstart != intervals.end())
                if((*itstart).start <= tmp)
                    itstart = intervals.erase(itstart);
                else break;
			}
			return intervals;
		}else if(itstart==intervals.end() && itend!=intervals.end())
		{
			(*itend).start = newInterval.start;
            int tmp1 = (*itend).start;
            int tmp2 = (*itend).end;
            itstart = intervals.begin();
    		while((*itstart).start != tmp1 && (*itstart).end != tmp2)
                if((*itstart).start >= tmp1 && (*itstart).end <= tmp2)
                     itstart = intervals.erase(itstart);
                else ++itstart;
			return intervals;
		}else if(itstart!=intervals.end() && itend==intervals.end())
		{
			(*itstart).end = newInterval.end;
            int tmp = newInterval.end;
            ++itstart;
			while(itstart != intervals.end())
            if((*itstart).start < tmp)
                itstart = intervals.erase(itstart);
            else break;
			return intervals;
		}else{
			vector<Interval>::iterator it=intervals.begin();
			for(; it!=intervals.end(); ++it)
				if((*it).start > newInterval.start)
					break;
			//--it;
			vector<Interval>::iterator it1 = intervals.insert(it,newInterval);
            while(it1 != intervals.end())
            {  
                if((*it1).end < newInterval.end)
                it1 = intervals.erase(it1);
    			else
                it1++;
            }
			return intervals;
		}
    }
};