# Problem Definition

## Description

Given an array A of integers, find the index of values that satisfy A + B = C + D, where A,B,C & D are integers values in the array

Note:

```plaintext
1) Return the indices `A1 B1 C1 D1`, so that
  A[A1] + A[B1] = A[C1] + A[D1]
  A1 < B1, C1 < D1
  A1 < C1, B1 != D1, B1 != C1

2) If there are more than one solutions, then return the tuple of values which are lexicographical smallest.

Assume we have two solutions
S1 : A1 B1 C1 D1 (these are values of indices int the array)
S2 : A2 B2 C2 D2

S1 is lexicographically smaller than S2 iff
  A1 < A2 OR
  A1 = A2 AND B1 < B2 OR
  A1 = A2 AND B1 = B2 AND C1 < C2 OR
  A1 = A2 AND B1 = B2 AND C1 = C2 AND D1 < D2
```

Example:

```plaintext
Input: [3, 4, 7, 1, 2, 9, 8]
Output: [0, 2, 3, 5] (O index)
```

If no solution is possible, return an empty list.

## Notes

1. [GeeksForGeeks similar problem](https://www.geeksforgeeks.org/split-array-two-equal-sum-subarrays/)