you are missing the most obvious one, no? Sum both lists and take the difference, that's the missing number, since the items are guaranteed unique

▲ vbezhenar a day ago | parent | next [-]

It is interesting for me to remember my very first programming task. The very first day I was introduced to programming with Pascal (I think I was 14), I was taught variables, assignments, arithmetic and was given a task to switch two variables (swap). I quickly solved it using third variable, but then I was asked to do it without third variable. It was very hard task for me, I spent few hours at home tackling it, but finally I solved it with a trick conceptually similar to XOR:

    a := a + b;
    b := a - b;
    a := a - b;

I'm still proud of little me and I always remember this solution when I encounter XOR tricks. I didn't knew about bitwise arithmetic at that time, but sometimes simple `+` can work just as well.

▲ a day ago | parent | prev | next [-]

[deleted]

▲ zeroq a day ago | parent | prev [-]

overflow

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criddell a day ago | parent [-]

Would a BigInteger sum still overflow?

	▲	Arnavion a day ago \| parent [-]
		It doesn't matter. Overflow is a non-issue as long as you have wrapping addition and subtraction operators, which C# does - regular `+` and `-` not inside `checked {}`. You don't need to reach for BigInteger.