using System;

public class Program
{

	public static int GetMissingNumberFromArray(int[] arr)
	{
		Console.WriteLine("=======================");
		int totalXor = 0;
		int totalArrXor = 0;

		for(int i = 1; i <= arr.Length + 1; i++){
			totalXor ^= i;
		}
		Console.WriteLine("totalXor : {0}", totalXor);


		foreach(int i in arr) totalArrXor ^= i;
		Console.WriteLine("totalArrXor : {0}", totalArrXor);

		return totalXor ^ totalArrXor;

	}

	public static int[] GetMissingTwoNumbers(int[] arr){

		int size = arr.Length + 2;
		Console.WriteLine("size : {0}", size);

		long totalSum = size*(size+1)/2;
		Console.WriteLine("totalSum : {0}", totalSum);

		long arrSum = 0;
		foreach(int i in arr) arrSum += i;
		Console.WriteLine("arrSum : {0}", arrSum);

		int pivot = (int)((totalSum - arrSum) / 2);
		Console.WriteLine("pivot : {0}", pivot);


		int totalXorRight = 0;
		int totalXorArrayRight = 0;
		int totalXorLeft = 0;
		int totalXorArrayLeft = 0;

		//find first array
		for(int i = 1; i <= pivot; i++) totalXorLeft ^= i;
		Console.WriteLine("totalXorLeft : {0}", totalXorLeft);

		//find second
		for(int i = pivot +1; i <= size; i++) totalXorRight ^= i;
		Console.WriteLine("totalXorRight : {0}", totalXorRight);

		foreach(int i in arr) {
			if(i <= pivot){
				totalXorArrayLeft ^= i;
			} else {
				totalXorArrayRight ^= i;
			}
		}

		Console.WriteLine("totalXorArrayLeft : {0}", totalXorArrayLeft);

		Console.WriteLine("totalXorRight : {0}", totalXorArrayRight);


		return new int[] {(totalXorLeft ^ totalXorArrayLeft), (totalXorRight ^ totalXorArrayRight)};
	}




	public static void Main()
	{
		int[] testArrayMissing2 = {1,2,5,6};

		int[] testArrayMissing1 = {1,2,4,5,6};

		int[] missingTwoNumbers = GetMissingTwoNumbers(testArrayMissing2);

		int missingOneNumber = GetMissingNumberFromArray(testArrayMissing1);


		Console.WriteLine("=======================");


		foreach(int i in missingTwoNumbers) Console.WriteLine("Number Missing : {0}", i);


		Console.WriteLine("--------------------");


		Console.WriteLine("Number Missing single : {0}", missingOneNumber);


	}
}