Solutions considering duplicates in the array.

solutions/java/ArrayPairSum.java

@@ -2,15 +2,25 @@
 import java.util.Arrays;
 import java.util.HashMap;
 
-
 public class ArrayPairSum {
-
+
+	/**
+	 * Does not consider duplicates of numbers
+	 * 
+	 * @param Sum
+	 *            . Example: 8
+	 * @param Integer
+	 *            array. Example: [3, 4, 5, 4, 4]
+	 * @return List of Integer pairs. Example: [[3, 5], [4, 4]]. Does not
+	 *         consider multiple occurrences of number 4.
+	 */
 	public ArrayList<int[]> getAllSumPairs(int k, int[] input) {
 		ArrayList<int[]> allSumPairs = new ArrayList<int[]>();
 		HashMap<Integer, Boolean> usedNumbers = new HashMap<Integer, Boolean>();
 		for (int i = 0; i < input.length; ++i) {
 			int difference = k - input[i];
-			if (usedNumbers.containsKey(difference) && !usedNumbers.get(difference)) {
+			if (usedNumbers.containsKey(difference)
+					&& !usedNumbers.get(difference)) {
 				int[] sumPair = new int[2];
 				sumPair[0] = input[i];
 				sumPair[1] = difference;
@@ -22,22 +32,88 @@ public ArrayList<int[]> getAllSumPairs(int k, int[] input) {
 		}
 		return allSumPairs;
 	}
-	
+
 	public static void printAllPairSums(ArrayList<int[]> allPairSums) {
 		String output = "[ ";
-		for (int[] pairSum: allPairSums) {
+		for (int[] pairSum : allPairSums) {
 			output += Arrays.toString(pairSum);
 			output += " ";
 		}
 		output += " ]";
 		System.out.println(output);
-	}	
-	
+	}
+
 	public static void main(String[] arg) {
 		ArrayPairSum a = new ArrayPairSum();
 		int[] input1 = { 3, 4, 5, 6, 7 };
 		printAllPairSums(a.getAllSumPairs(10, input1));
 		int[] input2 = { 3, 4, 5, 4, 4 };
 		printAllPairSums(a.getAllSumPairs(8, input2));
+
+		printAllPairSums(a.getAllSumPairsWithRep(10, input1));
+		printAllPairSums(a.getAllSumPairsWithRep(8, input2));
+
+		printAllPairSums(a.getAllSumPairsWithRepBetter(10, input1));
+		printAllPairSums(a.getAllSumPairsWithRepBetter(8, input2));
+	}
+
+	/**
+	 * Considers duplicates of numbers.
+	 * 
+	 * @param Sum
+	 *            . Example: 8
+	 * @param Integer
+	 *            array. Example: [3, 4, 5, 4, 4]
+	 * @return List of Integer pairs. Example: [[3, 5], [4, 4], [4, 4], [4, 4]].
+	 *         Considers multiple occurrences of number 4.
+	 * @complexity O(n2) best/worst case.
+	 */
+	public ArrayList<int[]> getAllSumPairsWithRep(int sum, int[] input) {
+		ArrayList<int[]> allSumPairs = new ArrayList<int[]>();
+		for (int i = 0; i < input.length - 1; i++) {
+			for (int j = i + 1; j < input.length; j++) {
+				int tSum = input[i] + input[j];
+				if (sum == tSum) {
+					int[] sumPair = new int[2];
+					sumPair[0] = input[i];
+					sumPair[1] = input[j];
+					allSumPairs.add(sumPair);
+				}
+			}
+		}
+		return allSumPairs;
+	}
+
+	/**
+	 * Considers duplicates of numbers.
+	 * 
+	 * @param Sum
+	 *            . Example: 8
+	 * @param Integer
+	 *            array. Example: [3, 4, 5, 4, 4]
+	 * @return List of Integer pairs. Example: [[3, 5], [4, 4], [4, 4], [4, 4]].
+	 *         Considers multiple occurrences of number 4.
+	 * @complexity O(n) best case - when all numbers are unique. O(n2) worst
+	 *             case - when all numbers are the same.
+	 */
+	public ArrayList<int[]> getAllSumPairsWithRepBetter(int sum, int[] input) {
+		ArrayList<int[]> allSumPairs = new ArrayList<int[]>();
+		HashMap<Integer, Integer> checker = new HashMap<Integer, Integer>();
+		for (int i = 0; i < input.length; i++) {
+			int diff = sum - input[i];
+			if (checker.containsKey(diff) && checker.get(diff) != null
+					&& checker.get(diff) > 0) {
+				for (int j = 0; j < checker.get(diff); j++) {
+					int[] sumPair = new int[2];
+					sumPair[0] = input[i];
+					sumPair[1] = diff;
+					allSumPairs.add(sumPair);
+				}
+				checker.put(input[i], checker.get(diff) + 1);
+			} else {
+				checker.put(input[i], 1);
+			}
+		}
+		return allSumPairs;
 	}
 }