/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
import java.util.HashMap;
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
 
    public static int getMaxDistance(int[] arr) {
        HashMap<Integer, Integer> firstIndexMap = new HashMap<>();
        int maxDistance = 0;
 
        for (int i = 0; i < arr.length; i++) {
            int num = arr[i];
 
            if (!firstIndexMap.containsKey(num)) {
                firstIndexMap.put(num, i); // store first occurrence
            } else {
                int distance = i - firstIndexMap.get(num);
                maxDistance = Math.max(maxDistance, distance);
            }
        }
 
        return maxDistance;
    }
 
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 2, 1, 4, 5, 1};
        System.out.println("Max distance: " + getMaxDistance(arr)); // Output: 7 - 0 = 7
    }
}
 
 

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