Sum of distances in tree

Given an undirected tree with n nodes labeled 0..n-1 and its edge list, return an array res where res[i] is the sum of the distances from node i to every other node. A naive BFS from each node is O(n^2); instead use the rerooting technique: one post-order pass computes subtree sizes and the answer for the root, then one pre-order pass propagates each node's answer to its children in O(1) using res[child] = res[parent] - size[child] + (n - size[child]). Return res. n can be up to 3e4.