first duplicate in array
import java.util.*;
class Main
{
// This function prints the first repeating element in arr[]
static void printFirstRepeating(int arr[])
{
// Initialize index of first repeating element
int min = -1;
// Creates an empty hashset
HashSet<Integer> set = new HashSet<>();
// Traverse the input array from right to left
for (int i=arr.length-1; i>=0; i--)
{
// If element is already in hash set, update min
if (set.contains(arr[i]))
min = i;
else // Else add element to hash set
set.add(arr[i]);
}
// Print the result
if (min != -1)
System.out.println("The first repeating element is " + arr[min]);
else
System.out.println("There are no repeating elements");
}
// Driver method to test above method
public static void main (String[] args) throws java.lang.Exception
{
int arr[] = {10, 5, 3, 4, 3, 5, 6};
printFirstRepeating(arr);
}
}