Sum Swap


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.

We are looking for two values, a and b, such that:
sumA - a + b = sumB - b + a
Doing some quick math:
2a - 2b = sumA - sumB
a - b = (sumA - sumB) / 2

Therefore, we're looking for two values that have a specific target difference: (sumA - sumB) / 2. The difference between the sums must be even to have a valid pair.
X. 
int[] findSwapValues(int[] arrayl, int[] array2) {
        Integer target= getTarget(arrayl, array2);
        if (target== null) return null;
        return findDifference(arrayl, array2, target);
}

/* Find a pair of values with a specific difference.*/
int[] findDifference(int[] arrayl, int[] array2, int target) {
        HashSet<Integer> contents2 = getContents(array2);
        for (int one : arrayl) {
                int two= one - target;
                if (contents2.contains(two)) {
                        int[] values = {one, two};
                        return values;
                }
        }

        return null;
}

/* Put contents of array into hash set. */
HashSet<Integer> getContents(int[] array) {
        HashSet<Integer> set= new HashSet<Integer>();
        for (int a : array) {
                set.add(a);
        }
        return set;
}

If the arrays are sorted, we can iterate through them to find an appropriate pair. This will require less space.
https://github.com/careercup/CtCI-6th-Edition/blob/39a4e384757c3716faba4492b7530f752669e812/Java/Ch%2016.%20Moderate/Q16_21_Sum_Swap/QuestionD.java
int[] findSwapValues(int[] arrayl, int[] array2) {
        Integer target = getTarget(arrayl, array2);
        if (target == null) return null;
        return findDifference(arrayl, array2, target);
}

int[] findDifference(int[] arrayl, int[] array2, int target) {
        int a = 0;
        int b = 0;

        while (a < arrayl.length && b < array2.length) {
                int difference = arrayl[a] - array2[b];
                /* Compare difference to target. If difference is too small, then make it
                 * bigger by moving a to a bigger value. If it is too big, then make it
                 * smaller by moving b to a bigger value. If it's just right, return this
                 * pair. */
                if (difference == target) {
                        int[] values = {arrayl[a], array2[b]};
                        return values;
                } else if (difference < target) {
                        a++;
                } else {
                        b++;
                }
        }
        return null;
}

int[] findSwapValues(int[] arrayl, int[] array2) {
        Integer target = getTarget(arrayl, array2);
        if (target== null) return null;

        for (int one : arrayl) {
                for (int two : array2) {
                        if (one - two== target) {
                                int[] values= {one, two};
                                return values;
                        }
                }
        }
        return null;
}

Integer getTarget(int[] arrayl, int[] array2) {
        int suml = sum(arrayl);
        int sum2 = sum(array2);
        if ((suml - sum2) % 2 != 0) return null;
        return (suml - sum2) / 2;
}

https://github.com/careercup/CtCI-6th-Edition/blob/master/Java/Ch%2016.%20Moderate/Q16_21_Sum_Swap/QuestionB.java
public static int[] findSwapValues(int[] array1, int[] array2) {
  int sum1 = sum(array1);
  int sum2 = sum(array2);
     
  for (int one : array1) {
    for (int two : array2) {
      int newSum1 = sum1 - one + two;
      int newSum2 = sum2 - two + one;
      if (newSum1 == newSum2) {
        int[] values = {one, two};
        return values;
      }
    }
  }
 
  return null;
}
https://github.com/careercup/CtCI-6th-Edition/blob/master/Java/Ch%2016.%20Moderate/Q16_21_Sum_Swap/QuestionA.java

int[] findSwapValues(int[] arrayl, int[] array2) {
        int suml sum(arrayl);
        int sum2 = sum(array2);
        for (int one : arrayl) {
                for (int two : array2) {
                        int newsuml = suml - one + two;
                        int newSum2 = sum2 - two + one;
                        if (newsuml == new5um2) {
                                int [] values = { one, two};
                        }
                }

                return values;
        }
        return null;
}

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