## Volume of n-ball

If we denote the Cartesian coordinate of a $n$-dimensional Euclidean space by a $n$-vector $\mathbf{x}$, then a $n$-ball centered at the origin with radius $r$ is the set of points that satisfy [more]

## 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]