Question

How to find the first repeating element in an array of integers with C#

Answer 1

using System;
using System.Collections.Generic; 

class Program
{
    public static int get_first_repeating_element(int[] arr) { 
        int x = -1; 
  
        HashSet<int> st = new HashSet<int>(); 
  
        for (int i = arr.Length - 1; i >= 0; i--) { 
            if (st.Contains(arr[i])) { 
                x = i; 
            } 
            else { 
                st.Add(arr[i]); 
            } 
        } 
      
        if (x != -1) 
            return arr[x]; 
          
        return -1; 
    } 
    static void Main()
    {
        int[] arr = new int[] {1, 2, 4, 5, 6, 5, 4, 3, 7}; 
    
        int n = get_first_repeating_element(arr); 
      
        if (n != -1) 
            Console.WriteLine("First repeating element is: " + n); 
        else
            Console.WriteLine("No repeating elements"); 
    }
}


/*
run:

First repeating element is: 4

*/

 

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