Find the smallest missing number

// C# program to find the smallest
// elements missing in a sorted array.
using System;

class GFG
{
    static int findFirstMissing(int []array,
                            int start, int end) 
    {
        if (start > end)
            return end + 1;

        if (start != array[start])
            return start;

        int mid = (start + end) / 2;

        // Left half has all elements from 0 to mid
        if (array[mid] == mid)
            return findFirstMissing(array, mid+1, end);

        return findFirstMissing(array, start, mid);
    }

    // Driver program to test the above function
    public static void Main() 
    {
        int []arr = {0, 1, 2, 3, 4, 5, 6, 7, 10};
        int n = arr.Length;
        
        Console.Write("smallest Missing element is : "
                    + findFirstMissing(arr, 0, n - 1));
    }
}

// This code is contributed by Sam007 

// C# program for above approach 
using System;

class GFG{
    
// Program to find Smallest  
// Missing in Sorted Array 
int findSmallestMissinginSortedArray(int[] arr)  
{  
    
    // Check if 0 is missing  
    // in the array 
    if (arr[0] != 0) 
        return 0; 
    
    // Check is all numbers 0 to n - 1  
    // are present in array 
    if (arr[arr.Length - 1] == arr.Length - 1) 
        return arr.Length; 
    
    int first = arr[0]; 
    
    return findFirstMissing(arr, 0, 
           arr.Length - 1,first); 
} 
    
// Program to find missing element  
int findFirstMissing(int[] arr , int start ,  
                     int end, int first)  
{ 
    
    if (start < end)  
    { 
        int mid = (start + end) / 2; 
        
        /*Index matches with value  
        at that index, means missing 
        element cannot be upto that point */
        if (arr[mid] != mid+first) 
            return findFirstMissing(arr, start,  
                                    mid, first); 
        else
            return findFirstMissing(arr, mid + 1,  
                                    end, first); 
    } 
    return start + first; 
}

// Driver code
static public void Main ()
{
    GFG small = new GFG(); 
    int[] arr = {0, 1, 2, 3, 4, 5, 7}; 
    int n = arr.Length; 
    
    // Function Call 
    Console.WriteLine("First Missing element is : " + 
    small.findSmallestMissinginSortedArray(arr)); 
}
}

// This code is contributed by avanitrachhadiya2155

using System;

public class Program
{
    // function to find the smallest missing element in a sorted array
    public static int FindFirstMissing(int[] arr, int n, int m)
    {
        // create an auxiliary array of size m with all elements set to 0
        int[] vec = new int[m];

        // iterate over the input array and set the corresponding element in vec to 1 if it is present in arr
        for (int i = 0; i < n; i++)
        {
            vec[arr[i]] = 1;
        }

        // iterate over the range 0 to m and return the first index where the corresponding element in vec is 0
        for (int i = 0; i < m; i++)
        {
            if (vec[i] == 0)
            {
                return i;
            }
        }

        // if all elements in the range are present, return m (the upper bound of the range)
        return m;
    }

    public static void Main()
    {
        // initialize an example array, compute its length, and set the upper bound of the range of elements
        int[] arr = { 0, 1, 2, 3, 4, 5, 6, 7, 10 };
        int n = arr.Length;
        int m = 11;

        // call the FindFirstMissing function and output the result to the console
        Console.WriteLine("Smallest missing element is " + FindFirstMissing(arr, n, m));
    }
}