CareerCup

struct Job
{
	int start;
	int end;
};

struct JobPoint
{
	bool operator<(const JobPoint& p)
	{
		return time != p.time ? time < p.time : (IsStart && (!p.IsStart));
	}

	int time;
	bool IsStart;
};

int MinimalVMs(const vector<Job>& jobs)
{
	vector<JobPoint> jps;
	for (const Job& job : jobs)
	{
		jps.emplace_back(JobPoint{ job.start, true });
		jps.emplace_back(JobPoint{ job.end, false });
	}

	sort(jps.begin(), jps.end());

	int max_num = 0, cur_num = 0;
	for (int i = 0; i < jps.size(); i++)
	{
		if (jps[i].IsStart)
		{
			cur_num++;
			max_num = max(max_num, cur_num);
		}
		else
			cur_num--;
	}

	return max_num;
}

put starttime and endtime in one array and sort it ( be able to differentiate which is start and which is end). Scan the array for concurrently running program and keep track of max value for the same. after complete of scan return the max value.

Add 2 array, one for start & other for end. Sort both the arrays.
starting from end index=0, compare the start time with end idx time.

int[] start=new int[array.Length];
int[] end=new int[array.Length];
for(int i=0;i< array.Length;i++)
{
	start[i]=array[i][0];
	end[i]=array[i][1];
}
Array.Sort(start);
Array.Sort(end);
int numofVM=0;
for (int i=0;i<array.Length;i++ )
{
If (start[i]<=end[endidx] )
	numofVM++;
 else 
 endidx+1; 
}
return numofVM;