HackerRank - ACM ICPC Practice Contest 2016 - New year present - first submission, a lot of issues, pass test case 1, 5, failed 0. Just rush in before completion of coding.

NewYearPresent_1stSubmission.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace NewYearPresent
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = Convert.ToInt32(Console.ReadLine());
            int[] arr = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);

            Console.WriteLine(calculate(n, arr)); 
        }
        
        /*
         * test c(6, 3) = 6 *5 *4/(3*2*1)
         */
        private static long calCombination(int n, int k)
        {
            long res = 1;
            for (int i = n; i >= (n - k + 1); i--)
                res *= i;

            for (int i = 1; i <= k; i++)
            {
                res /= i;
            }

            return res;
        }

        private static long calculate(int n, int[] arr)
        {
            int SIZE = 10000001; 

            int[] buckets = new int[SIZE]; 

            for(int i = 0;i < n; i++)
            {
                buckets[arr[i]]++; 
            }

            long count = 0; 
            for(int i=2; i< SIZE; i++)
            {
                int n2 = buckets[i];
                int sum = i; 

                // Try 2 - for example, n2 = 5, 1 4 1 4 5 5
                if (n2 >= 2)
                {
                    long m = calCombination(n2, 2);

                    int foundTwo = 1;
                    bool foundFirst = false;
                    bool foundSecond = false;
                    int  start = 1; 
                    while (foundTwo < 3)
                    {
                        for (int j = start; j < n2; j++)
                        {
                            int v1 = buckets[i];
                            if (v1 == 0 || v1 >= n2)
                                continue;

                            for (int k = j + 1; k < n2; k++)
                            {
                                int v2 = buckets[k];
                                if (v2 == 0 || Math.Abs(v1 + v2 - sum) > 0)
                                    continue;

                                if (foundTwo == 1)
                                {
                                    foundFirst = true;
                                    start = j; 
                                }
                                else if (foundTwo == 2)
                                    foundSecond = true; 
                            }
                        }
                        
                        foundTwo++; 
                    }

                    if(foundFirst && foundSecond)
                        count += m;  
                }

                // Try 3 - for example, n2 =5, 1 2 2 5 5 5
                if(n2>=3)
                {
                    long m = calCombination(n2, 3);
                    for (int j = 1; j < n2; j++)
                    {
                        int v1 = buckets[i]; 
                        if (v1 == 0 || v1>= n2)
                            continue; 

                        for (int k = j+1; k < n2; k++)
                        {
                            int v2 = buckets[k];                                  
                            if (v2 == 0 || (v1+v2) >= n2)
                                continue;

                            for (int l = k + 1; l < n2; l++)
                            {
                                int v3 = buckets[l]; 
                                if (buckets[l] == 0 || Math.Abs(v1+v2+v3-sum) > 0)
                                    continue; 
                                
                                count += m;
                            }
                        }
                    }
                }                
            }

            return count; 
        }
    }

    
}