Update shallowest_decomp_tree.hpp

Author: lrvideckis

library/trees/shallowest_decomp_tree.hpp

@@ -21,11 +21,12 @@ void shallowest(auto& adj, auto f) {
     return dp;
   };
   dfs(dfs, 0, 0);
-  for (vi vec : order | views::reverse)
+  auto cpy(adj);
+  adj.assign(n, {});
+  for (vi vec : order)
     for (int v : vec) {
       f(v);
-      for (int u : adj[v])
-        iter_swap(ranges::find(adj[u], v), rbegin(adj[u])),
-          adj[u].pop_back();
+      adj[v] = cpy[v];
+      for (int u : adj[v]) adj[u].push_back(v);
     }
 }