A Young tableau is a $\text{2D}$ array of integers increasing from left to right and from top to bottom. Any unfilled entries are marked with $\infty$, and hence there cannot be any entry to the right of, or below a $\infty$. The following Young tableau consists of unique entries.
$$\begin{array}{llll} \textbf{1} & \text{2}& \text{5} & \text{14} \\ \text{3} & \text{4} & \text{6} & \text{23} \\ \text{10} & \text{12} & \text{18} & \text{25} \\ \text{31} & \text{$\infty$} & \text{$\infty$} & \text{$\infty$} \\ \end{array}$$
When an element is removed from a Young tableau, other elements should be moved into its place so that the resulting table is still a Young tableau (unfilled entries may be filled with a $\infty$). The minimum number of entries (other than $1$) to be shifted, to remove $1$ from the given Young tableau is _____.
- $2$
- $5$
- $6$
- $18$
