CLA

void lca(int inl, int inr, int preRoot, int a, int b) {
if (inl > inr) return;
int inRoot = pos[pre[preRoot]], aIn = pos[a], bIn = pos[b];
if (aIn < inRoot && bIn < inRoot)
lca(inl, inRoot-1, preRoot+1, a, b);
else if ((aIn < inRoot && bIn > inRoot) || (aIn > inRoot && bIn < inRoot))
printf("LCA of %d and %d is %d.\n", a, b, in[inRoot]);
else if (aIn > inRoot && bIn > inRoot)
lca(inRoot+1, inr, preRoot+1+(inRoot-inl), a, b);
else if (aIn == inRoot)
printf("%d is an ancestor of %d.\n", a, b);
else if (bIn == inRoot)
printf("%d is an ancestor of %d.\n", b, a);
}