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Advent of Code 2020: "Encoding Error" - Day 9

Uh oh, either the ice cream at the airport was bad, or the cocktails are not good for you! How else can you explain that you hack the airplane systems with some paperclips and break the XMAS encryption, while the plane is airborne? The plane's on-board systems emits some cryptic numbers and your task is it to decrypt this. Wait, did I say task? Who gave this task to you? Oh well, please be careful, if you shorten a circuit you might as well crash your own plane.

Task 1: 25 numbers, followed by more numbers. The first 25 are the initial set, in the following numbers if you add two of the last 25 numbers the result might be he current number. You have to find the first one which is not the sum of two of the previous 25 numbers.

Tast 2: Now that you found the first number which does not add up, find a contiguous set of two or more numbers which add up to the result of task 1.

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