Revert "Ladder optimization (#83)"

This reverts commit a9ee2fa.

Author: lrvideckis

.verify-helper/timestamps.remote.json

@@ -70,7 +70,6 @@
 "tests/library_checker_aizu_tests/handmade_tests/dsu_size.test.cpp": "2024-09-22 18:42:16 -0500",
 "tests/library_checker_aizu_tests/handmade_tests/edge_cd_small_trees.test.cpp": "2024-09-21 13:04:45 -0500",
 "tests/library_checker_aizu_tests/handmade_tests/fib_matrix_expo.test.cpp": "2024-09-23 11:20:46 -0500",
-"tests/library_checker_aizu_tests/handmade_tests/lca_ladder_forest.test.cpp": "2024-10-17 18:24:12 -0700",
 "tests/library_checker_aizu_tests/handmade_tests/manacher.test.cpp": "2024-10-06 21:59:37 -0700",
 "tests/library_checker_aizu_tests/handmade_tests/merge_sort_trees.test.cpp": "2024-09-22 18:42:16 -0500",
 "tests/library_checker_aizu_tests/handmade_tests/mobius.test.cpp": "2024-09-19 12:57:45 -0700",
@@ -138,8 +137,6 @@
 "tests/library_checker_aizu_tests/trees/edge_cd_contour_range_update.test.cpp": "2024-09-22 18:42:16 -0500",
 "tests/library_checker_aizu_tests/trees/edge_cd_count_paths_per_length.test.cpp": "2024-09-21 13:04:45 -0500",
 "tests/library_checker_aizu_tests/trees/edge_cd_reroot_dp.test.cpp": "2024-09-21 13:04:45 -0500",
-"tests/library_checker_aizu_tests/trees/kth_node_on_path.test.cpp": "2024-10-17 18:24:12 -0700",
-"tests/library_checker_aizu_tests/trees/ladder_decomposition.test.cpp": "2024-10-17 18:24:12 -0700",
 "tests/library_checker_aizu_tests/trees/lca_all_methods_aizu.test.cpp": "2024-10-07 00:04:04 -0700",
 "tests/library_checker_aizu_tests/trees/lca_all_methods_lib_checker.test.cpp": "2024-10-07 00:04:04 -0700",
 "tests/library_checker_aizu_tests/trees/subtree_isomorphism.test.cpp": "2024-09-19 12:57:45 -0700"

library/trees/ladder_decomposition/ladder_decomposition.hpp

@@ -10,13 +10,13 @@
 //! @endcode
 struct ladder {
   int n;
-  vector<vi> b_tbl;
-  vi d, p, dl, idx_l, l_tbl;
+  vector<vi> b_tbl, l_tbl;
+  vi d, p, dl; //!< deepest leaf
   //! @param adj forest (rooted or unrooted)
   //! @time O(n log n)
   //! @space O(n log n) for b_tbl. Everything else is O(n)
   ladder(const vector<vi>& adj):
-    n(sz(adj)), d(n), p(n, -1), dl(n), idx_l(n) {
+    n(sz(adj)), l_tbl(n), d(n), p(n, -1), dl(n) {
     auto dfs = [&](auto&& self, int v) -> void {
       dl[v] = v;
       for (int u : adj[v])
@@ -29,10 +29,11 @@ struct ladder {
     rep(i, 0, n) {
       if (p[i] == -1) p[i] = i, dfs(dfs, i);
       if (p[i] == i || dl[p[i]] != dl[i]) {
-        int v = dl[i], len = (d[v] - d[i]) * 2;
-        idx_l[v] = sz(l_tbl) + d[v];
-        for (; v != -1 && len--; v = p[v])
-          l_tbl.push_back(v);
+        int leaf = dl[i];
+        vi& lad = l_tbl[leaf];
+        lad.resize(min(2 * (d[leaf] - d[i]), d[leaf] + 1),
+          leaf);
+        rep(j, 1, sz(lad)) lad[j] = p[lad[j - 1]];
       }
     }
     b_tbl = treeJump(p);
@@ -49,6 +50,6 @@ struct ladder {
     int bit = __lg(k);
     v = b_tbl[bit][v], k -= (1 << bit);
     int leaf = dl[v];
-    return l_tbl[idx_l[leaf] + k - d[v]];
+    return l_tbl[leaf][k + d[leaf] - d[v]];
   }
 };

library/trees/ladder_decomposition/linear_kth_par.hpp

@@ -9,11 +9,11 @@
 //! @space O(n)
 struct linear_kth_par {
   struct node {
-    int d, p = -1, dl, idx_j, idx_l;
+    int d, p = -1, idx, dl;
+    vi lad;
   };
   vector<node> t;
   vector<pii> j;
-  vi l_tbl;
   linear_kth_par(const vector<vi>& adj):
     t(sz(adj)), j(2 * sz(t)) {
     vi st;
@@ -25,7 +25,7 @@ struct linear_kth_par {
     };
     auto dfs = [&](auto&& self, int v) -> void {
       st.push_back(v);
-      t[v].idx_j = pos, t[v].dl = v;
+      t[v].idx = pos, t[v].dl = v;
       add_j();
       for (int u : adj[v])
         if (u != t[v].p) {
@@ -40,10 +40,12 @@ struct linear_kth_par {
     rep(i, 0, sz(t)) {
       if (t[i].p == -1) dfs(dfs, i);
       if (t[i].p == -1 || t[t[i].p].dl != t[i].dl) {
-        int v = t[i].dl, len = (t[v].d - t[i].d) * 2;
-        t[v].idx_l = sz(l_tbl) + t[v].d;
-        for (; v != -1 && len--; v = t[v].p)
-          l_tbl.push_back(v);
+        int leaf = t[i].dl;
+        vi& lad = t[leaf].lad;
+        lad.resize(
+          min((t[leaf].d - t[i].d) * 2, t[leaf].d + 1),
+          leaf);
+        rep(k, 1, sz(lad)) lad[k] = t[lad[k - 1]].p;
       }
     }
   }
@@ -55,9 +57,9 @@ struct linear_kth_par {
     case 2: return t[t[v].p].p;
     default:
       int i = 1 << __lg(k / 3);
-      auto [j1, j2] = j[(t[v].idx_j & -i) | i];
-      int up = t[v].d - t[j2].d <= k ? j2 : j1;
-      return l_tbl[t[t[up].dl].idx_l + k - t[v].d];
+      auto [j1, j2] = j[(t[v].idx & -i) | i];
+      int leaf = t[t[v].d - t[j2].d <= k ? j2 : j1].dl;
+      return t[leaf].lad[k + t[leaf].d - t[v].d];
     }
   }
 };