Get All the Products

Our next example is an algorithm that accepts an array of numbers and returns the product of every combination of two numbers.

For example, if we passed in the array, [1, 2, 3, 4, 5], the function returns:

 [2, 3, 4, 5, 6, 8, 10, 12, 15, 20]

This is because we first multiply the 1 by the 2, 3, 4, and 5. Then we multiply the 2 by the 3, 4, and 5. Next, we multiply the 3 by the 4 and the 5. And finally, we multiply the 4 by the 5.

Note something interesting: when we multiply, say, the 2 by the other numbers, we only have to multiply it by the numbers that are to the right of it. We don’t have to go back and multiply 2 by the 1, because that was already covered back when we multiplied by the 1 by the 2. So, each number only ...

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