## Simultaneous Equations in Two Unknowns

Consider this problem: A list of distinctive integers in random order is provided. The integer is in the range of $$1$$ to $$N$$ and there are $$N-1$$ integers provided, i.e. one integer in $$[1,N]$$ is not in the provided list. Find that number in $$O(1)$$ space and $$O(N)$$ time. [more]