const getSumIndices = (arr, target) => {
  if (target === undefined || arr.length < 2) return 0;

  const differences = {};
  const result = [];

  for (let i = 0; i < arr.length; i++) {
    const current = arr[i];

    if (differences[current] !== undefined) {
      result.push([differences[current], i]);
      delete differences[current];
    } else {
      const diff = target - current;

      if (!differences[current] && !differences[diff]) differences[diff] = i;
    }
  }

  return result;
};