static void Main(string[] args)
{
int[] items = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
var segmentTree = new SegmentTree <int>(items, (a, b) => a + b);
Console.WriteLine("18 == " + segmentTree.Query(2, 5));
Console.WriteLine("30 == " + segmentTree.Query(5, 8));
Console.WriteLine("22 == " + segmentTree.Query(3, 6));
segmentTree.ChangeValue(4, 0);
Console.WriteLine("13 == " + segmentTree.Query(2, 5));
Console.WriteLine("17 == " + segmentTree.Query(3, 6));
Console.ReadLine();
}