Solution to find swap number so that sum becomes equal

YogenRaii · YogenRaii · commit fc4e823d011f · 2019-06-23T18:27:40.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SumSwap.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SumSwap.java
@@ -0,0 +1,79 @@
+package com.eprogrammerz.examples.algorithm.crackingCoding;
+
+import org.junit.Test;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Given two arrays of integers, find a pair of values (one value from each array) that you can swap to give the two arrays the same sum.
+ */
+public class SumSwap {
+    /**
+     * EXAMPLE
+     * Input: {4, 1, 2, 1, 1, 2} and {3, 6, 3, 3}
+     * Output: {1, 3}
+     *
+     * @param arr1
+     * @param arr2
+     * @return
+     */
+    private int[] findSumSwapPair(int[] arr1, int[] arr2) {
+
+        /**
+         * sumA - a + b = sumB - b + a
+         * 2(a-b) = sumA-sumB
+         * (a-b) = (sumA-sumB)/2
+         */
+        Integer diff = getTarget(arr1, arr2);
+        if (diff == null) return null;
+
+        Set<Integer> set2 = getHashSet(arr2);
+
+        for (int i = 0; i < arr1.length; i++) {
+            int a = arr1[i];
+            int b = diff + a;
+            if (set2.contains(b)) {
+                return new int[]{arr1[i], b};
+            }
+        }
+
+        return null;
+    }
+
+    private Integer getTarget(int[] arr1, int[] arr2) {
+        int sum1 = findSum(arr1);
+        int sum2 = findSum(arr2);
+
+        int diff = Math.abs(sum1 - sum2);
+        if (diff % 2 != 0) return null;
+        return diff / 2;
+    }
+
+    private Set<Integer> getHashSet(int[] arr) {
+        Set<Integer> set = new HashSet<>();
+        for (int n : arr) {
+            set.add(n);
+        }
+        return set;
+    }
+
+    private int findSum(int[] arr) {
+        int sum = 0;
+        for (int n : arr) {
+            sum += n;
+        }
+        return sum;
+    }
+
+    @Test
+    public void testFindSumSwap() {
+        int[] arr1 = new int[]{4, 1, 2, 1, 1, 2};
+        int[] arr2 = new int[]{3, 6, 3, 3};
+        int[] res = findSumSwapPair(arr1, arr2);
+        assertArrayEquals(new int[]{4, 6}, res);
+    }
+}
