Coronavirus Spread

There are $N$ people on a street (numbered $1$ through $N$). For simplicity, we'll view them as points on a line. For each valid $i$, the position of the $i$-th person is $X_i$. It turns out that exactly one of these people is infected with the virus COVID-19, but we do not know which one. The virus will spread from an infected person to a non-infected person whenever the distance between them