least_frequest_element1.java

public static void main(String[] args) {

    int[] arr = {10,10,11,12,12,12};
    HashMap<Integer, Integer> hash = new HashMap<>();

    // saving frequency for each element in hashmap
    for (int element : arr) {

        if (hash.containsKey(element)) {
            int value = hash.get(element);
            value++;
            hash.put(element, value);
        } else {
            hash.put(element, 1);
        }

    }

    // getting minimum
    int min_Value = hash.get(arr[0]);
    int minKey = arr[0];

    for (int key : hash.keySet()) {

        if (hash.get(key) < min_Value) {
            min_Value = hash.get(key);
            minKey = key;
        }

    }

    System.out.println("least frequent element is "+minKey);

}