Max distance between same elements

class Solution {
    public int maxDistance(int[] arr) {
        int res = 0;
        HashMap<Integer, Integer> mp = new HashMap<>();

        for (int i = 0; i < arr.length; i++) {
            if (!mp.containsKey(arr[i]))
                mp.put(arr[i], i);
            else
                res = Math.max(res, i - mp.get(arr[i]));
        }
        return res;
    }
}