Write a function that, when passed an array and a target sum, returns, efficiently with respect to time used, two distinct zero-based indices of any two of the numbers, whose sum is equal to the target sum. If there are no two numbers, the function should return null.
For example, findTwoSum([ 3, 1, 5, 7, 5, 9 ], 10) should return an array containing any of the following pairs of indices:
- 0 and 3 (or 3 and 0) as 3 + 7 = 10
- 1 and 5 (or 5 and 1) as 1 + 9 = 10
- 2 and 4 (or 4 and 2) as 5 + 5 = 10
- Example case: Exception
- Distinct numbers with and without solutions: Exception
- Duplicate numbers with and without solutions: Exception
- Performance test with a large array of numbers: Exception
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