void findZigZagSequence(vector < int > a, int n)
{
	sort(a.begin(), a.end());
	int mid = n/2;  // 1st change
	swap(a[mid], a[n-1]);
	int st = mid + 1;
	int ed = n - 2;  //2nd change
	
   while(st <= ed)
   {
		 swap(a[st], a[ed]);
		 st = st + 1;
		 ed = ed - 1; //3rd change
	}
	....
}