At least One

We define $f(A)$ as the minimum positive integer $X$ such that the following condition holds: - For each $i$ ($1 \le i \le |A|$), there exists $j \ne i$ ($1 \le j \le |A|$), such that $|A_i - A_j| \le X$. For arrays of size $1$, i.e. $|A| = 1$, we define $f(A) = 0$. For other arrays, it can be proven there exists at least one such integer. --- You are given an integer $N$. Let $B = [1, 2, 3, \