finished q1

challenge1/Question1.java

@@ -0,0 +1,60 @@
+package com.example.challenge1;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class Question1 {
+
+    private static void findPairs(int[] testArray, int targetSum) {
+        // ASSUMPTIONS:
+        // 1. values in testArray range from 1 - (targetSum - 1)
+
+
+        // The first attempt I made involved nested loops.
+        // I suspected it would be faster to use a dictionary of some kind so I researched
+        // the question and found out
+        // 1. it is
+        // 2. the Java name for a dict is a map
+
+        HashMap<Integer, Integer> pairMap = new HashMap<>();
+
+        // variable used to handle values that are half of targetSum
+        int duplicate = 0;
+
+        for (int i : testArray) {
+            // count number of values that are exactly half of targetSum
+            if (i == targetSum - i) { duplicate++; }
+
+            // every possible pair is added to map
+            pairMap.put(i, targetSum - i);
+        }
+
+        for (int i = 0; i < targetSum; i++) {
+            // removes duplicates from map as well as pairs that don't exist
+            // ex: { 5 } will not print out (5, 1) since 1 is not in array
+
+            // half of targetSum is dealt with later
+            if (pairMap.containsValue(i) && pairMap.containsKey(i) && i != targetSum - i) {
+                pairMap.remove(i);
+            }
+        }
+
+        // remove half of targetSum from map if there isn't more than one in array
+        if (duplicate < 2) {
+            pairMap.remove(targetSum / 2);
+        }
+
+        for (Map.Entry<Integer, Integer> i : pairMap.entrySet()) {
+            System.out.println("(" + i.getKey() + ", " + i.getValue() + ")");
+
+        }
+
+    }
+
+    public static void main(String[] args) {
+        int[] testArray = {2, 4, 5, 1, 3, 5, 4};
+        int targetSum = 6;
+
+        findPairs(testArray, targetSum);
+    }
+}