main {

prepare_lca();
if (N!=-1) {
 build_segement_tree(1,0,N-2); //a[0..n-1]
}
int Q=read();
while(Q-->0) {
 int j=x;
 int x=read()-1;
 int y=read()-1;
 if (x!=y) {
   J= get(1, 0, N-2, x, y-1);
 }
 println(j);
}

}

in build_segement_tree
..
if (tl==tr) t[v]=lca(tl,tl+1);

Segment tree is an overkill. Sparse table does the work easily. Without any corner cases.