Tree: node (color ) has children (color ) and (color ). Node has child (color ). Process leaf : set = {}, answer = . Process node : take set from child which is {}, add color . Set = {, }, answer = .
Process leaf : set = {}, answer = . Process node : child has larger subtree (size vs ). Take set {, } from child . Merge {} from child . Add color . Final set = {, , }, answer = .