public static long Solve_Bit_Dfs(BinaryIndexedTree bit, List <int>[] adj, int node, int n, int k)
{
var count = bit.Get(Math.Max(1, node - k), Math.Min(n, node + k));
bit.SetDiff(node, 1);
foreach (var child in adj[node])
{
count += Solve_Bit_Dfs(bit, adj, child, n, k);
}
bit.SetDiff(node, -1);
return(count);
}