Challenge 115 Intermediate http://www.reddit.com/r/dailyprogrammer/comments/15wm48/132013_challenge_115_intermediate_sumpairings/

Challenge115.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.InputMismatchException;
import java.util.List;
import java.util.Scanner;

/**
 * Linear Time Solution
 * 
 * 14 <br>
 * 10 -8 2 1 4 -9 6 1 9 -10 -5 2 3 7 <br>
 * 7 <br>
 * 
 * @author SplashAttacks
 */
public abstract class Challenge115 {
  @SuppressWarnings("serial")
	private static class CountingHashMap extends HashMap<Integer, Integer> {
		public Integer put(Integer key) {
			int count = 1;
			if (containsKey(key)) {
				count = get(key) + 1;
			}
			return super.put(key, count);
		}

		/**
		 * Returns the key.
		 * 
		 * @param key
		 * @return
		 */
		@Override
		public Integer remove(Object key) {
			Integer intKey = (Integer) key;
			Integer count = get(intKey);
			if (count == null) {
				return null;
			} else if (count == 1) {
				return super.remove(intKey);
			} else {
				put(intKey, --count);
				return count;
			}
		}
	}

	private static class Criteria {
		private final List<Integer> array;

		public Criteria(List<Integer> array) {
			this.array = array;
		}

		public List<Pair<Integer, Integer>> getPairs(int number) {
			return process(number);
		}

		private List<Pair<Integer, Integer>> process(int number) {
			CountingHashMap countingMap = new CountingHashMap();
			for (Integer element : array) {
				countingMap.put(element);
			}
			List<Pair<Integer, Integer>> result = new ArrayList<Pair<Integer, Integer>>();
			for (Integer element1 : array) {
				Integer element2 = number - element1;
				if (countingMap.remove(element1) != null
						&& countingMap.remove(element2) != null) {
					result.add(new Pair<Integer, Integer>(element1, element2));
				}
			}
			return result;
		}

		@Override
		public String toString() {
			return "Criteria [array=" + Arrays.toString(array.toArray()) + "]";
		}
	}

	private static class Pair<U, T> {
		private final U element1;
		private final T element2;

		public Pair(U element1, T element2) {
			this.element1 = element1;
			this.element2 = element2;
		}

		public U getElement1() {
			return element1;
		}

		public T getElement2() {
			return element2;
		}

		@Override
		public String toString() {
			return "(" + element1 + ", " + element2 + ")";
		}
	}

	private static class RobotInput extends Challenge115 {
		private List<Integer> array;

		public RobotInput(Integer... array) {
			this.array = new ArrayList<Integer>(Arrays.asList(array));
		}

		@Override
		public List<Integer> getArray() {
			return array;
		}

		public void setArray(List<Integer> array) {
			this.array = array;
		}
	}

	private static class UserInput extends Challenge115 {
		@Override
		public List<Integer> getArray() {
			int arraySize;
			String stringArray;
			try (Scanner scanner = new Scanner(System.in)) {
				System.out.println("Array Size: ");
				arraySize = Integer.parseInt(scanner.nextLine().trim());
				System.out.println("Array: ");
				stringArray = scanner.nextLine();
			}
			List<Integer> result = new ArrayList<Integer>();
			for (String element : stringArray.split(" ")) {
				result.add(Integer.parseInt(element.trim()));
			}
			if (arraySize != result.size()) {
				throw new InputMismatchException("Given array size "
						+ arraySize + " does not match array size "
						+ result.size() + ".");
			}
			System.out.println("Array: " + Arrays.toString(result.toArray()));
			return result;
		}

		public void go() {
			int number;
			try (Scanner scanner = new Scanner(System.in)) {
				System.out.println("Enter number: ");
				System.out.println(scanner.nextLine());
				number = scanner.nextInt();
			}
			go(number);
		}
	}

	public static void main(String[] args) {
		Challenge115 challenge = new RobotInput(10, -8, 2, 1, 4, -9, 6, 1, 9,
				-10, -5, 2, 3, 7);
		challenge.go(7);
		challenge.go(2);
		// UserInput challenge = new UserInput();
		// challenge.go();
	}

	private Criteria criteria;

	public abstract List<Integer> getArray();

	public void go(int number) {
		if (criteria == null) {
			setNewCriteria();
		}
		System.out.println("Looking for " + number + " pairs.");
		for (Pair<Integer, Integer> pair : criteria.getPairs(number)) {
			System.out.println(pair);
		}
	}

	public void setNewCriteria() {
		this.criteria = new Criteria(getArray());
	}

	public void setNewCriteria(List<Integer> array) {
		this.criteria = new Criteria(array);
	}
}