1.java

public static void main(String[] args) {
    AbstractPurchase purchases[] = {...};
    Arrays.sort(purchases);
    print(purchases);
    /* http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#binarySearch(byte[],%20byte)
     * binarySearch return index of the search key, if it is contained in the array; 
     * otherwise, (-(insertion point) - 1). Use it by create comparator without return 0
     * (equals) section. binarySearch with this comparator always return insertion point.
     */
    final long SEARCH_COST = 90000;
    Comparator<AbstractPurchase> comp = new Comparator<AbstractPurchase>() {

        @Override
        public int compare(AbstractPurchase o1, AbstractPurchase o2) {
            if (o1.getCost() > SEARCH_COST) {
                return -1;
            }
            return 1;
        }
    
    };
    int f = Arrays.binarySearch(purchases, null, comp);
    /* Insertion point reverse transformation */
    f = -f - 1;
    if (f < purchases.length && purchases[f].getCost() == SEARCH_COST) {
        int l = f + 1;
        while (l < purchases.length && purchases[l].getCost() == SEARCH_COST) {
            l++;
        }
        System.out.printf("[%d,%d)", f, l);
    } else {
        System.out.println("NOT FOUND");
    }
}