public void insert(int el) {
        this.arr[el - 1] = el;
    }
Design a dictionary data structure in which search, insertion, and deletion can all be processed in O(1) time
in the worst case.
You may assume the set elements are integers drawn from a finite set 1, 2, .., n, and initialization can take O(n) time.
java8/src/main/java/com/shekhargulati/tadm/ch03/Problem3_4.java