icecream-parlor: Given a list of prices for the flavors of ice cream, select the two that will cost all of the money they have.

gistfile1.txt

import java.util.*;

class Scratch {
    public static void main(String[] args) {
        // https://www.hackerrank.com/challenges/icecream-parlor/problem
        // solved!

        // Given a list of prices for the flavors of ice cream,
        // select the two that will cost all of the money they have.
        int m;
        List<Integer> costs;
        List<Integer> r;

        m = 6;
        costs = Arrays.asList(1,3,4,5,6);
        r = icecreamParlor(m, costs);
        // The two flavors that cost 1 and 5 meet the criteria.
        // Using 1-based indexing, they are at indices 1 and 4.
        System.out.println("r = " + r);
    }

    public static List<Integer> icecreamParlor(int m, List<Integer> arr) {
        List<Integer> results = new ArrayList();

        // O(n)
        Map<Integer, Integer> numsIndex = new HashMap();
        for (int i=0; i< arr.size(); i++) {
            int i1 = i+1;
            int n = arr.get(i);

            int otherN = m-n;
            if (numsIndex.containsKey(otherN)) {
                int otherIndex = numsIndex.get(otherN);
                // System.out.printf("a:%d @ %d b:%d @ %d \n",n,i1,otherN,otherIndex);
                if (i1 <= otherIndex) {
                    results.add(i1);
                    results.add(otherIndex);
                } else {
                    results.add(otherIndex);
                    results.add(i1);
                }
            }
            // after search or we get ourselves
            numsIndex.put(n, i1);
        }

        return results;
    }
}