public static int minimumDistances(List<Integer> arr) {
    Map<Integer, LinkedList<Integer>> itemDistanceMap = new HashMap<>();
    for(int i=0;i<arr.size(); i++) {
        int key = arr.get(i);
        if(itemDistanceMap.get(key) == null) {
            LinkedList<Integer> indices = new LinkedList<>();
            indices.add(i);
            itemDistanceMap.put(key, indices);
        } else {
            itemDistanceMap.get(key).add(i);
        }
    }

    int minDistance = Integer.MAX_VALUE;

    Collection<LinkedList<Integer>> distances = itemDistanceMap.values();

    for(LinkedList<Integer> distanceLst : distances) {
        if(distanceLst.size() > 1) {
            int distance = distanceLst.get(1) - distanceLst.get(0);
            minDistance = distance < minDistance ? distance : minDistance;
        }
    }        
    return minDistance == Integer.MAX_VALUE ? -1 : minDistance;
}