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] inas [1,2],[3,10],[12,16].

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

 

       思路：本题与《Merge Intervals》类似，可以沿用其中的思路：首先将new interval插入到interval数组中，排序，然后重新merge即可。

       但是本题因为有这样的预设：”the intervals were initially sorted according to their start times.”。intervals数组已经是按照start排好序的了，所以，可以按照《Merge Intervals》思路，一次遍历即可解决问题：在merge遍历原数组时，找到new interval合适的插入位置，加入到merge过程中。

       但是这种算法需要考虑的边界条件有点多，思路上也不如《Merge Intervals》清晰。下面的代码就是这种思路的实现：

struct Interval* insert(struct Interval* intervals, int intervalsSize, struct Interval newInterval, int* returnSize) 
{
	struct Interval *res = NULL;
	int reslen = 0;
	int laststart, lastend;

	struct Interval *curnode = NULL;
	int i = 0, j = 0;
	int flag = 0;

	if(intervalsSize == 0)
	{
		res = calloc(1, sizeof(struct Interval));
		res->start = newInterval.start;
		res->end = newInterval.end;
		*returnSize = 1;
		return res;
	}

	//新插入节点与第一个元素的start进行比较
	if(newInterval.start < intervals[0].start)
	{
		laststart = newInterval.start;
		lastend = newInterval.end;
		j = 0;
	}
	else
	{
		laststart = intervals[0].start;
		lastend = intervals[0].end;
		j = 1;
	}
	
	for(i = j; i < intervalsSize; i++)
	{
		if(newInterval.start > intervals[i].start || flag)
		{
			curnode = intervals+i;
		}
		else
		{
			curnode = &newInterval;
			flag = 1;
			i--;
		}

		if(curnode->start <= lastend)
		{
			if(curnode->end > lastend)
			{
				lastend = curnode->end;
			}
		}
		else
		{
			reslen++;
			res = realloc(res, reslen*sizeof(struct Interval));
			res[reslen-1].start = laststart;
			res[reslen-1].end = lastend;
			laststart = curnode->start;
			lastend = curnode->end;
		}
	}

	//新插入节点的start比数组中所有元素的start都要大
	if(flag == 0)
	{
		if(newInterval.start <= lastend)
		{
			if(newInterval.end > lastend)
			{
				lastend = newInterval.end;
			}
		}
		else
		{
			reslen++;
			res = realloc(res, reslen*sizeof(struct Interval));
			res[reslen-1].start = laststart;
			res[reslen-1].end = lastend;
			laststart = newInterval.start;
			lastend = newInterval.end;
		}
	}


	reslen++;
	res = realloc(res, reslen*sizeof(struct Interval));
	res[reslen-1].start = laststart;
	res[reslen-1].end = lastend;

	*returnSize = reslen;
	return res;
}