void Build(int n)
{
Array.Sort(pos, (a, b) => (a.X == b.X ? a.Y - b.Y : a.X - b.X));
int[] a = new int[n];
HashSet <int> set = new HashSet <int>();
for (int i = 0; i < n; i++)
{
a[i] = pos[i].Y - pos[i].X;
set.Add(pos[i].Y - pos[i].X);
}
int num = set.Count;
int[] b = new int[num];
int index = 0;
foreach (int element in set)
{
b[index++] = element;
}
Array.Sort(b);
BIT bit = new BIT(num + 1);
for (int i = n - 1; i >= 0; i--)
{
int poss = BinarySearch(b, a[i]) + 1;
int j = bit.query(poss);
if (j != -1)
{
int dis = Math.Abs(pos[i].X - pos[j].X) + Math.Abs(pos[i].Y - pos[j].Y);
edges.Add((dis, pos[i].Id, pos[j].Id));
