Dual Distance

### Read problem statements in [Vietnamese](https://www.codechef.com/download/translated/JUNE21/vietnamese/DUALDIST.pdf), Given a tree with $N$ nodes, answer $Q$ queries of the following type: - $a, b$ (where $a \ne b$) which asks you to calculate $\sum_{i=1}^{N} \min(\mathrm{dist}(i, a), \mathrm{dist}(i, b))$ where $\mathrm{dist}(x, y)$ is the number of edges on the shortest path between th