fix

Author: lrvideckis

tests/library_checker_aizu_tests/handmade_tests/count_paths.test.cpp

@@ -60,6 +60,34 @@ vector<vector<ll>> naive(const vector<vi>& adj) {
   }
   return cnts_naive;
 }
+#include "../../../kactl/content/numerical/FastFourierTransform.h"
+#include "../../../library/trees/edge_cd.hpp"
+//! @param adj unrooted, connected tree
+//! @returns array `num_paths` where `num_paths[i]` = # of
+//! paths in tree with `i` edges. `num_paths[1]` = # edges
+//! @time O(n * logφ(n) * log2(n))
+//! @space this function allocates/returns various vectors
+//! which are each O(n)
+vector<ll> count_paths_per_length(const vector<vi>& adj) {
+  vector<ll> num_paths(sz(adj));
+  if (sz(adj) >= 2) num_paths[1] = sz(adj) - 1;
+  edge_cd(adj,
+    [&](const vector<vi>& cd_adj, int cent, int split) {
+      vector<vector<double>> cnt(2, vector<double>(1));
+      auto dfs = [&](auto&& self, int u, int p, int d,
+                   int side) -> void {
+        if (sz(cnt[side]) == d) cnt[side].push_back(0.0);
+        cnt[side][d]++;
+        for (int c : cd_adj[u])
+          if (c != p) self(self, c, u, 1 + d, side);
+      };
+      rep(i, 0, sz(cd_adj[cent]))
+        dfs(dfs, cd_adj[cent][i], cent, 1, i < split);
+      vector<double> prod = conv(cnt[0], cnt[1]);
+      rep(i, 0, sz(prod)) num_paths[i] += llround(prod[i]);
+    });
+  return num_paths;
+}
 int main() {
   cin.tie(0)->sync_with_stdio(0);
   for (int n = 1; n <= 100; n++) {