Check if an Array is a permutation of numbers from 1 to N

using System;

public class GFG {
    // Function to check if an Array is a
    // permutation of numbers from 1 to N
    public static bool IsPermutation(int[] arr, int n)
    {
        // Check for each element from
        // 1 to N in the array
        for (int i = 1; i <= n; i++) {
            bool found = false;
            for (int j = 0; j < n; j++) {
                if (arr[j] == i) {
                    found = true;
                    break;
                }
            }
            // If any element is not found,
            // array is not a permutation
            if (!found) {
                return false;
            }
        }

        // All elements found, array
        // is a permutation
        return true;
    }

    // Driver's code
    public static void Main(string[] args)
    {
        int[] arr = { 1, 2, 5, 3, 2 };
        int n = arr.Length;

        if (IsPermutation(arr, n)) {
            Console.WriteLine("Yes");
        }
        else {
            Console.WriteLine("No");
        }
    }
}

// This code is contributed by Samim Hossain Mondal.

// C# Program to decide if an
// array represents a permutation or not
using System;
using System.Collections.Generic;

class GFG{
 
// Function to check if an
// array represents a permutation or not
static bool permutation(int []arr, int n)
{
    // Set to check the count
    // of non-repeating elements
    HashSet<int> hash = new HashSet<int>(); 
 
    int maxEle = 0;
 
    for (int i = 0; i < n; i++) {
 
        // Insert all elements in the set
        hash.Add(arr[i]);
 
        // Calculating the max element
        maxEle = Math.Max(maxEle, arr[i]);
    }
 
    if (maxEle != n)
        return false;
 
    // Check if set size is equal to n
    if (hash.Count == n)
        return true;
 
    return false;
}
 
// Driver code
public static void Main(String []args)
{
    int []arr = { 1, 2, 5, 3, 2 };
    int n = arr.Length;
 
    if (permutation(arr, n))
        Console.WriteLine("Yes");
    else
        Console.WriteLine("No");
}
}

// This code is contributed by Princi Singh

// C# Program to decide if an
// array represents a permutation or not
using System;

public class GFG
{
    // Function to check if an
    // array represents a permutation or not
    public static bool permutation(int[] arr, int n)
    {
          //sorting the array
          Array.Sort(arr);

          //traversing the array to find if it is a valid permutation ot not
          for (int i = 0;i < n;i++)
          {
              //if i+1 element not present
              //or dublicacy is present
              if (arr[i] != i + 1)
              {
                  return false;
              }
          }

          return true;
    }
    
    internal static void Main()
    {
        int[] arr = {1, 2, 5, 3, 2};
        int n = arr.Length;

        if (permutation(arr, n))
        {
            Console.Write("Yes");
            Console.Write("\n");
        }
        else
        {
            Console.Write("No");
            Console.Write("\n");
        }
    }
}

//This code is contributed by bhardwajji

using System;

public class Gfg
{
  public static bool permutation(int[] arr, int n)
  {
    
    // create a boolean array to keep track of which numbers
    // have been seen before
    bool[] x = new bool[n];

    // initialize the boolean array with false values
    for (int i = 0; i < n; i++)
    {
      x[i] = false;
    }

    // check each number in the array
    for (int i = 0; i < n; i++)
    {
      // if the number has not been seen before, mark it
      // as seen
      if (x[arr[i] - 1] == false)
      {
        x[arr[i] - 1] = true;
      }
      // if the number has been seen before, the array
      // does not represent a permutation
      else
      {
        return false;
      }
    }

    // check if all numbers from 1 to n have been seen in
    // the array
    for (int i = 0; i < n; i++)
    {
      // if a number has not been seen in the array, the
      // array does not represent a permutation
      if (x[i] == false)
      {
        return false;
      }
    }

    // if the array has passed all checks, it represents a
    // permutation
    return true;
  }

  public static void Main()
  {
    // initialize the array to be checked
    int[] arr = { 1, 2, 3, 4, 5 };
    int n = arr.Length;

    // check if the array represents a permutation
    if (permutation(arr, n))
    {
      Console.WriteLine("YES");
    }
    else
    {
      Console.WriteLine("NO");
    }
  }
}