solves intersection of 2 arrays II

Author: anishLearnsToCode

src/IntersectionOfTwoArraysII.java

@@ -0,0 +1,46 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class IntersectionOfTwoArraysII {
+    public static int[] intersect(int[] array1, int[] array2) {
+        Map<Integer, Integer> frequency1 = getFrequencies(array1);
+        Map<Integer, Integer> frequency2 = getFrequencies(array2);
+        return intersection(frequency1, frequency2);
+    }
+
+    private static Map<Integer, Integer> getFrequencies(int[] array) {
+        Map<Integer, Integer> result = new HashMap<>();
+        for (int element : array) {
+            result.put(element, result.getOrDefault(element, 0) + 1);
+        }
+        return result;
+    }
+
+    private static int[] intersection(Map<Integer, Integer> frequency1, Map<Integer, Integer> frequency2) {
+        List<Integer> result = new ArrayList<>();
+        for (Map.Entry<Integer, Integer> entry : frequency1.entrySet()) {
+            int number = entry.getKey();
+            int frequency = entry.getValue();
+            if (frequency2.containsKey(number)) {
+                addNumber(result, number, Math.min(frequency, frequency2.get(number)));
+            }
+        }
+        return toArray(result);
+    }
+
+    private static void addNumber(List<Integer> list, int number, int frequency) {
+        while (frequency-- > 0) {
+            list.add(number);
+        }
+    }
+
+    private static int[] toArray(List<Integer> list) {
+        int[] array = new int[list.size()];
+        for (int index = 0 ; index < array.length ; index++) {
+            array[index] = list.get(index);
+        }
+        return array;
+    }
+}