Write a C++ program to find the first repeating element in an array of integers

#include<iostream>
using namespace std;
 int first_repeating_element(int array1[], int s1)
{
    int min_val = -1;
 
    set<int> result;
 
    for (int i = s1 - 1; i >= 0; i--)
    {
        if (result.find(array1[i]) != result.end())
            min_val = i;
 
        else   
            result.insert(array1[i]);
    }
 
    if (min_val != -1)
        return array1[min_val];
    else
        return 0;
}

int main()
{
    int array1[] = {3, 1, 5, 1, 5, 7, 9, 7, 9};
    int fre;
 
    int s1 = sizeof(array1) / sizeof(array1[0]);
    
    cout << "Original array: ";
    
    for (int i=0; i < s1; i++) 
    cout << array1[i] <<" ";
    
    fre = first_repeating_element(array1, s1);
    cout <<"\nFirst repeating  element: " << fre;
    return 0; 
}