HackerRank world code sprint #6 - study code #1 - BrontTrousle

BrontTrousle_studyCode1.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Numerics;
class Solution {
    static void Main(String[] args) {
        var t = int.Parse(Console.ReadLine());
        for(var test = 0; test < t; test++){
            var nkb = Console.ReadLine().Split(' ');
            var n = BigInteger.Parse(nkb[0]);
            var k = BigInteger.Parse(nkb[1]);
            var b = BigInteger.Parse(nkb[2]);
            Console.WriteLine(BuyBoxes(n, k, b));
        }
    }
    
    static string BuyBoxes(BigInteger n, BigInteger k, BigInteger b){
        BigInteger count = 0;
        BigInteger sum = 0;
        if(n < b*(b + 1) / 2){
            return "-1";
        }
        if( n > (k*(k + 1) / 2 - (k - b)*(k - b + 1) / 2)){
            return "-1";
        }
        BigInteger diff = n - b*(b + 1) / 2;
        
        var sb = new StringBuilder();
        var tochange = b;
        var maxvalue = k;
        while(tochange > 0){
            BigInteger change = BigInteger.Min(maxvalue - tochange, diff);
            sb.Append(tochange + change);
            sum += tochange + change;
            count++;
            sb.Append(' ');
            diff -= change;
            maxvalue = tochange + change - 1;
            tochange--;
        }
        if(sum != n){
            throw new NotImplementedException();
        }
        if(count != b){
            throw new Exception();
        }
        return sb.ToString().TrimEnd();
    }
}