What are the different ways to find missing numbers in a sorted array without any inbuilt functions using C#?

There are three methods as written below −

• In the first method

  Use the formula n(n+1)/2 that counts the number of elements and then need to subtract from the elements in the array.

• In the second method

  Create a new array and traverse through the entire array and make the number false whichever is found.

• In the third method

  Use Xor operation. which gives the missing number.

Example

 Live Demo

using System; namespace ConsoleApplication{    public class Arrays{       public int MissingNumber1(int[] arr){          int totalcount = 0;          for (int i = 0; i < arr.Length; i++){             totalcount += arr[i];          }          int count = (arr.Length * (arr.Length + 1)) / 2;          return count - totalcount;       }       public int MissingNumber2(int[] arr){          bool[] tempArray = new bool[arr.Length + 1];          int element = -1;          for (int i = 0; i < arr.Length; i++){             int index = arr[i];             tempArray[index] = true;          }          for (int i = 0; i < tempArray.Length; i++){             if (tempArray[i] == false){                element = i;                break;             }          }          return element;       }       public int MissingNumber3(int[] arr){          int result = 1;          for (int i = 0; i < arr.Length; i++){             result = result ^ arr[i];          }          return result;       }    }    class Program{       static void Main(string[] args){          Arrays a = new Arrays();          int[] arr = { 0, 1, 3, 4, 5 };          Console.WriteLine(a.MissingNumber1(arr));          Console.WriteLine(a.MissingNumber2(arr));          Console.WriteLine(a.MissingNumber3(arr));          Console.ReadLine();       }    } }

Output

2 2 2